Well with P4 and NT, the character select screen will be perfectly balanced. Not sure if they intend on releasing more, but as it stands, the roster is looking quite nice.
I think that the roster's in a good spot now with the addition of Marie Rose, and think that Phase-4 & Nyo-Tengu may be a little unnecessary. I personally would like a roster as balanced as possible with all character's tech being sufficiently explored. I've never seen the appeal of 50+ rosters and prefer the roster sizes of VF5:FS or SCV for instance.
I look at TTT2's roster and it's just a clusterfuck. USF4's roster is getting pretty damn big now too. In terms of gameplay & personality, I welcome Nyo-Tengu though. Phase-4 is pretty much just a Kasumi clone with some gimmicky teleports.