I'd be down for some Lance Reddick as Professor X. I also think Denzel would kill it, but he is great in just about everything.
Personally I think there are only a handful of characters that shouldn't change, Superman, Batman, Spiderman, Wolverine, Captain America and maybe the Hulk. To me these characters have all transcended the art form that spawned them and I think even the most basic person would know who these characters are and have an idea of what they look like. I think with characters of this magnitude if you want to do something different than I really like the approach taken by Logan and Spiderman: Into the Spiderverse. Miles definitely held his own and X-23 was a breakout star. Even still I'd go see any movie starring these characters regardless of my personal opinions.