MMR isn't too complicated.
League of legends system is very solid *it isnt very good in a team based game like 5v5 LoL*
The ladder system would allow people to rank up, without being numerically ranked for the most part. This will allow us to accomplish, S class players playing with A, and S tier players. Allow for growth. Continually playing
against more experienced players based on on your performance, win loss ratio. In a 1v1 game, no one will hold you back. this isnt 2006.
Internet isnt what it used to be. To combat lag, make sure the games are hosted on a server and not client side. have good network optimization.
This is 2013! Internet is fantastic, a majority of north america has fast enough internet to make this work as long as it stays away from P2P.
However if nintendo makes the game international there will be some problems, they should have seperated networks, universal server works for MK7 3ds. But not a game where every MS counts.