lem hitting a steel block
fall (potentially fatal), or propel safely back down?
You can copy what the jumper does: Allow a queued shimmier assignment to execute here, otherwise fall. Then your two upwards-flying skills (propeller and jumper) are consistent with each other.
Feeling: NL/SLX allow climbers to jump off walls, swimmers to jump out of water, ..., then why not propellers to shimmy, too.
Yes, the skills should be about one thing and have few rules (as WillLem says), yet be able to play roles of swiss army knifes (as mobius says). The potential falling (with or without allowed shimmier assignment) has its uses, too: Combine with floater, combine with a higher lemming splatforming underneath in the meantime, ...
-- Simon