Well Summoner is going to have...

Ruin series of spells
Outburst (AoE damage skill) upgrade
Carbuncle support skills ( Some kind of shield as well as a Carbuncle version of devotion)
5 summons with their own elemental themed attacks/actions for the Summoner
Aetherflow generator skills that proc a buff for a single use of Ruin 4
Fester and Painflare
Enkindle Bahamut/Phoenix
Physick and Resurrection
Deathflare as an action under Bahamut
New active buff under Phoenix

What Summoner seems to have lost...

All DoTs
Tridisaster
Dreadwyrm/Phoenix Trance
Use of standard Egi's and their skills.
Egi Assaults

Everything revolves completely around summoning now.

Which makes you wonder how the leveling progress will be for new players.

It's really looking at endgame that there is going to be a gameplay loop of a 5 summon system with Bahamut/Phoenix refreshing Ifrit/Titan/Garuda.