"A lemming can exit if it is on the ground, or is performing an action where it is not subject or only partially subject to gravity"
This seems like a good rule; it catches the floater, glider and swimmer, and also explains why a reacher and a jumper would be able to exit.
Both reacher and jumper are
actions which a lemming is performing (hence my suggestion of "active" state) -
it's absolutely feasible that a lemming could jump into a midair exit. Or, at the very least, it's as feasible as a lemming being able to float/glide into a midair exit. Therefore, keeping the behaviour maintains this consistency.
Personally, I would always expect a lemming to exit upon contact with an exit's trigger area, regardless of how they got there, and even more regardless of whether or not there is terrain beneath the exit's trigger. Of course, this is already
not the case in most versions of Lemmings, so as a player I've adapted to the various other behaviours that the game presents.
Again, it ultimately comes down to preference (or, if you prefer, expectation); those who don't want the behaviour will find arguments against it, and those who want the behaviour will find arguments for it. What's needed is a clear rule which has everything covered, so it's good that this is the direction the conversation is going in.
It'll be interesting to see what prevails.
As far as I am aware, there are no levels yet requiring Shimmiers or Jumpers to exit while in that state
There is a level in
Lemminas which requires a reacher to be able to exit. It's an easy enough fix if the decision is to disallow the behaviour though, and the solution will in fact be the same so replays won't break.
EDIT:
That's fine: Gravity merely accelerates downwards; gravity doesn't imply that affected things are already moving downwards. Thus, albeit without sleeping over it, your idea appears to catch the essence even for a non-exitable jumper/reacher.
This direction has converged really nicely.
I don't quite understand, please can you re-word this...?