This idea was imagined with the potential onset of a hybrid role system as hinted at by the developers and with current knowledge of an increased level cap and addition of new Egis with the 3.0 expansion. SMN would be reclassified as a hybrid role in this case focusing on DPS with the ability to add support to the team. Some of the current Egi's see some ability changes. The reasoning behind this is that with the onset of 6 total Egi's each one will need to have their own niche to fit or else the current trend of just using one of them will continue.
In addition to this idea SMN will gain a stance, Astral Flow, which will lower casting times for all "Summon" abilities (I'm thinking to around 2 or 3s), reduce MP costs of Summon I-VI, reduce the Summoner's DPS while increasing the Egi's DPS and allow you to combo your summons.
This stance is primarily to give players a play-style option. Without the stance up SMN will play like the current FFXIV SMN model using DoTs and Fester for the bulk of damage and using the appropriate pet as the situation demands. With Astral Flow up it will play like the classic FF SMN model calling out all of their pets for burst AoE damage and supporting their pet's damage with their DoTs. The DPS of both play-styles will be similar but the Astral Flow style will likely be a bit weaker to account for the support it adds and its large focus on AoE damage. This weakness is found mostly in the fact that Aetherflow charges will be used on Energy Drain instead of Fester to sustain the rotation and there will likely be times where DoT's fall off.
The combo system works in that summoning an Egi while another one is present will reduce the recast/cooldown of Enkindle in order to get more uses of it (I'm thinking to around 10s or so). They will only be boosted as dictated by the current elemental wheel as found in game:
"The spark of Lightning ignites when it strikes, and thus Fire is born."
-If Summon III is used while Ramuh is active Enkindle's recast/cooldown is reduced.
"The heat of Fire renders to ash all that it touches, and thus Earth is born."
-If Summon II is used while Ifrit is active Enkindle's recast/cooldown is reduced.
"The density of Earth shuns sun and harbors cold, and thus Ice is born."
-If Summon VI is used while Titan is active Enkindle's recast/cooldown is reduced.
"The armor of Ice melts away, and thus Water is born."
-If Summon IV is used while Shiva is active Enkindle's recast/cooldown is reduced.
"The moistness of Water mists and rises, and thus Wind is born."
-If Summon is used while Leviathan is active Enkindle's recast/cooldown is reduced.
"The gusts and sighs of Wind gather the clouds, and thus Lightning is born."
-If Summon V is used while Garuda is active Enkindle's recast/cooldown is reduced.
Abilities:
Potencies left out due to future rebalancing of current Egi's.
* Denotes Enkindle.
4:
Summon: Summons a caster-type pet to fight by your side.
4:
Windblade: Deals wind damage with a potency of X. Recast: 3s.
4:
Shockwave: Deals wind damage with a potency of X. Additional Effect: 15-yalm knockback. Recast: 90s.
20:
Aerial Slash: Deals wind damage with a potency of X to target and all enemies nearby it. Recast: 30s.
40:
Contagion: Extends duration of damage over time effects already cast by master by Xs. Recast: 60s.
*50:
Aerial Blast: Deals wind damage with a potency of X to target and all enemies nearby it. Astral Flow: Recast: 300.
Garuda: Largely unchanged. This the go-to pet for sustained DPS when a fight will be long or MP intensive or when there will be a lot of target switching as she is a ranged unit. Astral Flow: Primarily used to extend your DoT's so you have more time for summoning and will otherwise be used for AoE damage.
15:
Summon II: Summons a tank-type pet to fight at your side (Titan). Melee.
15:
Rock Buster: Delivers an attack with a potency of X. Additional Effect: Increased enmity. Recast: 3s.
15:
Mountain Buster: Delivers an attack with a potency of X to all nearby enemies. Additional Effect: Increased enmity. Recast: 15s.
20:
Earthen Ward: Decreases damage suffered by pet by 20% for 20s. Recast: 120s.
40:
Landslide: Delivers an attack with a potency of X. Additional Effect: Pacification for Xs. Recast: 40s.
*50:
Earthen Fury: Deals earth damage with a potency of X to all nearby targets. Additional Effect: Razed earth for 15s. Recast: 300s.
Titan: Largely unchanged. This still functions as your solo tanking pet. Astral Flow: Used for AoE damage.
30:
Summon III: Summons an attacker-type pet to fight at your side (Ifrit). Melee.
30:
Burning Strike: Delivers an attack with a potency of X. Recast: 3s.
30:
Crimson Cyclone: Delivers an attack with a potency of X to all nearby enemies. Recast: 30s.
30:
Crimson Howl: Increases potencies and reduces duration of damage over time effects already cast by master by Xs. Recast: 60s.
40:
Flaming Crush: Delivers an attack with a potency of X. Additional Effect: Fire damage with a potency of X for Xs. Recast: 90s.
*50:
Inferno: Deals fire damage with a potency of X to all enemies in a cone before it. Additional Effect: Fire damage over time with potency of X for 15s. Recast: 300s.
Ifrit: Several changes. This is now the go-to pet for burst DPS when a fight will be short or will have little worry for MP. Astral Flow: Primarily used to apply 2 quick DoTs, one of which AoE.
55:
Summon IV: Summons a healer-type pet to fight at your side (Leviathan). Ranged.
55:
Spinning Dive: Delivers a ranged attack with a potency of X. Additional Effect: A water ball drops on and heals the party member with the lowest HP for X potency. Recast: 3s.
55:
Spring Water: Heals party member with lowest HP for X potency. If target is raised to 100% HP the excess healing is given to the next party member with the lowest HP. The process continues up to a maximum of one half of the current party's size. A single party member can only be healed by it once per use. Recast: 30s.
55:
Water Spout: Creates a geyser under Leviathan for Xs which heals all who enter with a potency of X every tick. Recast: 60s.
55:
Tidal Roar: Increases HP restored by spells or actions by X% on nearby party members for Xs. Recast: 120s.
*55:
Tidal Wave: Deals water damage with a potency of X to all enemies in a cone before it. Additional Effect: Party members within 5y of targets that receive damage from this attack will be healed with a potency of X. Recast: 300s.
Leviathan: New addition. This will be the Summoner's healing pet. Overall DPS will see about a 20% loss due to having only one attack. Primarily used when a healer goes down or runs out of MP or other emergency support situations. Astral Flow: Used for AoE DPS and an AoE heal.
60:
Summon V: Summons a caster support-type pet to fight at your side (Ramuh). Ranged.
60:
Shock Strike: Deals lightning damage with a potency of X. Recast: 3s.
60:
Thunderstorm: Deals lightning damage with a potency of X to enemies within Xy of Ramuh. Additional Effect: Stun for Xs. Recast: 30s.
60:
Thunderbolt: Deals lightning damage with a potency of X. Additional Effect: Stun for Xs. Recast: 10s.
60:
Chaotic Strike: Deals lightning damage with a potency of X. Additional Effect: Terror for Xs. Recast: 120s.
*60:
Judgment Bolt: Deals lightning damage to enemies within Xy of Ramuh. Additional Effect: Paralyze for Xs. Recast: 300s.
Ramuh: New addition. This will be the Summoner's enemy-focused support pet. Primarily used for stun duty to alleviate the need for PLDs. Astral Flow: Used for AoE DPS and paralysis.
65:
Summon VI: Summons an attacking support-type pet to fight at your side (Shiva). Melee.
65:
Axe Kick: Delivers an attack with a potency of X. Recast: 3s.
65:
Frost Armor: Creates a barrier around the party member with the lowest HP% that prevents damage of all sources totaling X% of target's maximum HP for Xs. Recast: 30s.
65:
Mesmerize: Puts target and enemies within 5y to sleep for Xs. Cancels auto-attack upon execution. Recast: 20s.
65:
Diamond Storm: Creates a designated area around Shiva in which party members will only suffer X% of all damage inflicted for Xs. Additional Effect: Deals Ice damage with a potency of X to enemies within the designated area. Recast: 120s.
*65:
Diamond Dust: Deals ice damage to enemy and nearby targets. Additional Effect: Creates a barrier around party members within Xy of enemies damaged by this ability that prevents physical damage totaling X% of target's maximum HP for Xs. Recast: 300s.
Shiva: New addition. This will be the Summoner's party-focused support pet. Primarily used for her shield effects akin to SCH. Astral Flow: Used for AoE DPS and a shield effect.
70:
Astral Flow: Summon I-VI MP costs are reduced by X% and casting times are reduced to Xs. Summoner damage dealt is reduced by X% and pet damage dealt is increased by X%. Each summon using the elemental wheel order Fire>Earth>Ice>Water>Wind>Lightning>Fire will reduce the recast/cooldown of Enkindle to Xs. Effect ends upon re-use. MP Cost: X.
Astral Flow rotation will look something like this although you can start with any Egi: Dot's > Garuda > Contagion > Aerial Blast > Ramuh > Judgement Bolt > Ifrit > Flaming Crush > Inferno > Titan > Landslide > Earthen Fury > Shiva > Diamond Storm > Diamond Dust > Leviathan > heals/buffs as needed > Tidal Wave. Rouse/Spur/Fester to be used whenever they're up. DoT's re-applied as they fall off preferably during an Enkindle animation. Aetherflow charges will likely be spent on Energy Drain instead of Fester to facilitate Enkindles.