I think a part of the problem with Soma, if it isn't biased favouritism on part of the developers, would be the soul system having so many souls to use. But if the number of enemies were cut down, people would complain. Such a no win situation.
Anyway... I'd like to see a lot of characters: Hammer (his name was yelled out in a few voice files), the Saturn version of the older Maria (if for variety in the gameplay), Albus, Juste, Nathan (I'd imagine implementing the DSS would be a pain however), Eric Lecarde (maybe give him a few subweapons), Stella and Loretta (have it so that the two need to be synchronized and equipped, though some new animations would have to be made), and possibly Maxim too for a ninja character.
As for stages, a Rondo of Blood stage should have been a must, considering that Rondo of Blood is one of the most celebrated games in the franchise. I'd also like to see a stage or two for Bloodlines, the Saturn version of SotN, Harmony of Dissonance, Super Castlevania IV and Circle of the Moon.
For the other characters, at least give Maria her Egg subweapon from Rondo, and I'd suggest a new spell or two for Yoko because although she's supposed to be a shout out to Sypha, while having only the three spells was acceptable in the NES days, these days that's seen as lacking.
Sorry if I dragged on too long...