Also, the workaround would fall apart if a lemming is falling into an exit from splat height - fall distance is carried over when going through a teleporter.
I know - you're talking to the person who made the Pit Lems levels "The long way down" and "Controlled overload", after all, which made excessive use of this part of the game physics...
Yes, exactly. So you'd need an updraft as well in that scenario. Eeesh!
...and in turn, this would have been exactly my suggestion on how to handle this problem, and I knew nobody would figure this out more quickly than WillLem himself!
After all, nobody has used updrafts on exit triggers more frequently than him, as far as I know. In fact, hard-to-see updrafts in front of exits were something I myself had criticised about Lemminas, even though these updrafts were actually set to "overwrite" to display layered on top of the exit, so not really "invisible", just hard to spot against the background of the exit object itself.
That said, you could also use an anti-splat pad on the exit, too.
Since for this application, terrain would be required within the exit trigger area anyway.
And I think the anti-splat pad in this context is a great example to illustrate the large overlap (and thus redundancy) between regular exits and the proposed vortex:
The difference only matters in very few cases.
With anti-splat pads, the fact that you could place them in the air somewhere with no terrain inside, so that lemmings could fall through them without having their fall height reset like from an updraft was a crucial enough difference in my book, alongside anti-splat pads having existed before and being the logical counterpart to splat pads.
Vortices however would be an entirely new object, while basically just being a subtype of exit (like locked / non-locked exits). At this point it seems to me like regarding teleporters, Arty's super-teleporter, and the future prospect of portals as three different types of objects. Or like the non-lethal Stoners and Bombers you proposed a long time ago.