There's been a lot of buzz around tumblr and IG about how much Sebastian Stan looks like a young Mark Hamill:

I'd call that a fair comparison... he really does share the same features, uncannily so in some photos. So of course, this has also led to a lot of fans calling for him to play Luke's son or more plausibly to play a young Luke in a flashback scene.
One intrepid Star Wars/Sebastian fan put up this post on IG, and look at who commented on it at the bottom:

(Yes, that's his official IG account.)
He had four auditions! I wonder if they were call-backs or if he just kept showing up hoping to get a role out of sheer stubborn determination, like Steve Rogers trying to get into the Army seventeen times. It's intriguing and makes me wonder if he did at least leave a favorable impression (especially if they were of the call back nature where they wanted to see him, rather than the other way around), a strong enough one that might lead to a future role in the franchise, as he hopes. But can you imagine JJ Abrams et al looking at him for, say, Poe Dameron's part but having to turn him down because he does look so much like Luke Skywalker it might skew the entire plot... or at least mess with the audience's expectations so much that it leads to a complete FUBAR when it's revealed he doesn't really have anything to do with the Skywalker clan other than being a damn good pilot in the Rebellion. *g*
(Sidenote: I get so tickled at the teenage girls now suddenly going nuts on tumblr fangirling over young Harrison Ford and Mark Hamill, who *I* fangirled over back in the day... it's just so
odd. But fun. Definitely fun.)