Masks are a huge no-go. They're not going to try to hide their identities. These suits were created and used for practical reasons. Masks aren't.
As for what I'd like to see in the sequel, well, if it takes place in the sixties or seventies, I say don't fix what's not broken. These were my favorite suits by far. Maybe a few subtle changes (like materials and different customizations.) I say, if any changes, they should be on the level of the changes between X1 and X2; not much, just cleaner lines, better proportions, design-wise, etc. But definitely keep the same basic concept, and keep the blue/yellow/black scheme. From what I know from the working script during filming - it wasn't mentioned in the final cut - Beast had actually created the suits after his split with Raven, so, one night. And you can tell because his own suit was created for his new, blue form. So, maybe the next sets
will be more advanced versions that Beast had a bit more time to work on.
EDIT: Oh, and X's! At the very least the belt buckle.