If he’s simply referring to the Sentinels, then that’s one thing – we might take that for granted. I wouldn’t expect him to cast a real robot.*
But maybe he isn’t. Here’s the exact exchange between Singer and MTV:
Singer: I definitely want to use this [peformance capture, animated character] technology again, and I might even be using some of it in a different way in X-Men. I don’t wanna say how, yet, but I’m definitely using some of this technology on X-Men which I never used in any of the other X-Men films.
MTV: Are you talking about creating a fully CGI character in Days of Future Past?
Singer: That’s the thing I don’t want to talk about. I’m not sure. I’m doing research on it now.
I really don’t think he’s talking about a Sentinel unless it’s a Sentinel with personality, tied to a particular actor. So I’m thinking it might be a mutant… but which one?
Perhaps it will be a way to save Nicholas Hoult from horrendous Beast make-up, or to introduce a new mutant that wouldn’t work so well with old-school latex techniques?
If I were to go crazy out on a limb and think of a truly unusual application I’d speculate that Jennifer Lawrence might get to play Mystique even when she doesn’t look like Mystique, or maybe when she’s adult Mystique. That would definitely be an interesting application of the tech.
*Though this has worked out well in the past, with several shots in Real Steel using real bots and the Chris Cunningham work in Judge Dredd proving impressive. And Robot and Frank shows how an actor in a suit can really nail it.