In the interests of preventing SLX being swamped with an L2-like mess of very similar skills, I can't help pointing out that if SLX will have NL's new objects, then any time you want a one-use swimmer, you can put a permanent skill remover object on the other side of a water pond. There would be some potential for backrouting levels by bypassing the remover, but this can be prevented with careful design of the terrain and skillset.
With a suitable terrain setup, a glider can also cross a water pond in one direction while being unable to cross in the other.