The Varkolian and Worldbane Eidolons seem to be the best out of the Other Eidolons for their Ultimates. Stonecoiled + Bonelord + Varkolian might be BIS for Shinobi. Maybe Gold-Clawed depending on what "Buffed" refers to if not Atk Speed.
i'm sure they will buff or add new content similar to trial of embers where we can get huge amount of resource from previous season with relatively low effort.