I wouldn't mind seeing Hayden in the ST. All he would need is the right acting coach to get him in the good frame of mind for his scenes and secondly he needs good dialogue. People seem to forget only amazing actors give vastly greater performances than the actual writing allows. I mean even Samuel L. Jackson wasn't good in the PT and he's an overall great actor.

As it pertains to Ewan I wouldn't want to see him in the ST for the sake of continuity. But an Obi-Wan spin off film with him at the helm seems far better in theory than a Han Solo movie.