They should definitely give Bahamut the Phoenix treatment along with any future Demi summons since it'll make the phases feel a lot better, but they also need to compensate for the lack of mobility and weaving phases we'll lose, and the longer downtime waits.
We've already lost one Dreadwyrm Trance for Phoenix that SMN suddenly went from most mobile to least mobile caster. If they actually planted the Demi summons in place then maybe mobility won't be an issue anymore, but Egi Assault weaving for the most part would be without the reliability of Dreadwyrm Trance.