Re-using a channel / slot without killing the note would trigger a Legato in a monophonic plugin that is able to do legato. That is absolutely not what might be desirable when pressing a completely unaffiliated key. That is why my plugin sends Note-off(s) in that case.
Of course you are right that the purpose of MPE and legato is contradicting.
OTOH, this seems to work (with the Rise), as it is exactly what the video with the two Celli shows.
But trying to accomplish this in accordance with or even without the help pf the keyboard during a channel reducing preprocessing tool seems rather hopeless
-Michael