In my opinion 5-man would detract from the game. There's an extra life built into every loop, after all, and 5-man settings would dictate never going for it. That seems a bit arbitrary to me, and forced.
I'd prefer changing the extra lives settings to only award a single extra life at 20K or 30K and sidestep having to watch every inp for exactly 5 deaths.
We already have one pain-in-the-ass-to-adjudicate game with Vs SMB, I don't think we need another. Also, I don't feel like everybody and their momma is going to be marathoning PP -- it's a tricky game that can eat fistfuls of lives at a time.