My guesses?
-Snake would rise back up above Diddy. Marth, Wario, and ICs may very well rise above Diddy in the future with no MK around as well, though how fast would be unknown. I'd say Wario is the least likely out of the trio I mentioned and would take a good influx of mains to pull it off. Falco I honestly don't know. I could see him rising up above Diddy, but I could also see him dropping below the ICs. He's an oddball to me when you take out MK.
-Pikachu would drop back down to high tier. D3 may climb back up above Lucario, but Lucario would be happy with MK gone as well...really hard to tell how that trio would stack.
-G&W would be both buffed and nerfed by no more MK. Obviously, no MKs is good, but more Snakes is bad. I think considering other characters and how much they would be buffed by no MK, G&W would overall drop. Toon Link would rise probably a couple of spots. ZSS...I don't have a clue.
-Fox would drop. Wolf would drop with him, but not as much. DK would drop due to increase in D3, but not by much. Peach would be top of mid tier. ROB would rise a bit, possibly a fair bit. Sonic and Ike would both get a noticeable boost, possibly slightly more in Ike's case. I don't think Pit would really move much at all when considering all of the other movement around him.
-As for the other characters, I don't know. Ness might drop slightly due to an increase of Marths, same with Lucas, but how much is unknown. Who would benefit more, Yoshi or PT? I'm leaning towards PT overall, but I don't know. I'd be willing to believe that Link would rise a spot over Falcon, but it's low tier. That area is already fairly jumbled up with lots of "don't know, I guess I'll throw him here" occurring.
Obviously, when it comes to stages, there would be a lot less crying over RC and Brinstar. More stages could be more easily accepted.