A easy one first, is on the scoreboard to show when a teammate drops to put a DNF (did not finish) marker, and maybe the round in which they dropped out.

Also, for MMR- since wins are really important, is it possible to take into account if a win/loss is shorthanded?

Solo queue is tough, but those two would at least be a bit helpful without being too impactful. Right now the amount of people who drop in ranked lower elo is really high.