This mod is gonna live for a longgggg time, probably until you can no longer find an old wii model to play it on (but i bet they'll some how fix that problem too cuz the PMBR are ****ing awesome) i would like to compare it too other mods that have lived to become real games (dota, counter strike, etc.) unfortunately Nintendo is an ass to their smash fans and that will certainly not happen ever, but the amount of people playing and getting interested in PM just keeps on growing and growing, especially since PM even works as a safe haven for those smash fans that want to play their favorite character just to realize they suck total ass in every iteration of smash bros.
This mod will live, and if they even put ONE new character in the next release the amount of casuals that will flock to this game will be incredible. BUT i can see brawl getting annihilated between the growing popularity of melee and especially PM, not to mention all the casuals will eventually move on to smash 4 whether it be on 3DS or Wii U.