Well, I think in one of Faust's post fight speeches against Testament, he tells that summoning is one of his hobbies aswell, so maybe (is Faust would ever be on it) he'll have an army of bizarre things and strange looking flowers or so, maybe even Fanny looking units. And dunno either Zappa could share army with him or he'll have his own little army of ghosts.
Well about Overture, I'm also against it, but gonna give it a shot anyway, who knows maybe I'll ending up liking it. Many of you are telling that Daisuke is considering X and XX non canon, he and Arc hasn't stated yet that they will stop making games of this "sidestory". (if you're gonna go "OHH THEY DO!" on me, please post a link to verify your information, thanks) So don't lose hopes, if they do stop it, then I'll go and cry in a corner because I loved that "sidestory". (and the gameplay, I love fighting games and I consider GG the best) For now I think Overture storyline is to keep Ishiwatari happy in his pants, I know there's gonna be some kind of demand for continuing X-XX storyline maybe as what he calls it, a "non-canon sidestory". I just hope it's that way...
If not...
May God helps us all...