So... what's the ruling on this?
My thoughts, simplified as much as possible:
1) The Swimmer is a very under-powered Skill as it stands.
The ability to exit water from underneath would double its possible use-cases (no, a Shimmier is not comparable because a Shimmier can
only exit terrain from underneath; whereas if what I'm proposing gets passed, Swimmers will be able to exit the water in both directions).
2) It would make physical sense.
Water is a soft obstacle, and if the body of water were in a zero-gravity environment, things
would be able to exit it from any direction.
Swimmers need a good boost. If you pass this one, I promise I'll never mention Splat/Anti-Splat Fields again!