Summoner in this game is channeling the energy of the Primals and that's exactly what we do with Dreadwyrms Trance by absorbing Bahumats Ether. I hope we get to channel the other 6 primals.
No new Egis since there is no elemental wheel caster damage has the same effect its just applied differently so Leviathan, Ramuah and Shiva egi won't add anything different than the current three. Ifrit Egi is the only actual new summon we get as a Summoner otherwise Titan and Garuda Egi are just re skinned Carbuncle and Topaz. So instead of wasting 3 new abilities on re skinned Egis they decided to give us more Summoner abilities and flesh out the current Egis. Adding Leviathan, Ramuh and Shiva Egi with glamours is a good idea because we can just re skin the Egis ourselves and slot them in on the hot bar and we have 3 more summons complete with new animations.