I have a feeling half of these characters will have minor but memorable part in the movie.
Yeah I don't really see Bryan giving all of these characters the same amount of screentime but it doesn't mean they can't shine. So far, there's only 1 new character that is for sure getting a big role in the movie and that is Dinklage's character since he's going to be the main antagonist of this movie, let's see if he gets a sidekick or a henchman. I see Omar Sy having a supporting role if he's indeed playing Bishop and I see Bingbing having a role like Nightcrawler if she will teleport the team to the past. I think it will be like this:
Lead roles = Wolverine, Professor X, Magneto, Mystique?, Dinklage
Supporting roles = Beast (just like in FC), Storm, Rogue, Iceman, Shadowcat, Omar (if he's Bishop), Blink (if she's the time traveler)
Minor roles = Colossus (just like in X2), Booboo (Banshee/Riptide treatment), President Nixon
And if we count the "6 character spots left", I think only one of those six could have a lead role in the movie. Then the rest are just either supporting role, minor role or a cameo.