Although I think new trees could be fun and interesting, I just don't think Blizz can pull it off.
Speaking of interrupts or mechanics in general, I think it would be cool if every class got some kind of boost for dealing with a mechanic. Maybe some cooldowns are reduced, or 10 seconds of +crit, or whatever, just some kind of boost so that mechanics aren't just something you deal with because you have to, but something you look forward to a little bit more.