Exceptions are probably the least canonical part of (the sequential part of) the ML-Scala continuum. Maybe it will fall by the wayside. With HKTs monadic error handling becomes relatively painless. I have no strong opinion on this matter.

I think sequential programming won't be the deciding factor. Error handling becomes more difficult when concurrency is involved. It's unclear whether the monadic approach scales to concurrency. The Erlang experience seems to suggest that more complicated approaches might be appropriate.