Perhaps, and I am working on complete hypotheticals here, maybe this is the reason the whole Gambit thing has been such a hush hush issue. If (and this is a huge huge if) this guy has been cast as Gambit, perhaps they want to keep it a bit quiet because of the internet effect. "WHAT? HE'S GAMBIT??? THAT IS THE SUXXORS!!!!!!!!!" (See reaction to "script review")
Maybe they want to keep it quiet to see exactly what this guy can do. If it works, great. If not, it is not the end of the world, because they can simply cut the guy out of the film or reduce his role to a cameo.
Now this is a strictly hypothetical situation here. If the guy is telling the truth. If he has become a menber of the cast. If he has been cast as Gambit. It could all end up being complete BS and we have specualted ourselves to death for nothing.