I don't think it will, but it is certainly in the realm of possibility. For Brawl+ to actually be accepted as the new standard, several things would have to happen first. First, the Brawl metagame must slowly grind to a halt as, either Metaknight dittos become commonplace or no new mechanics are discovered and incorporated into the game. From there (if it doesn't completely die out), Metaknight will probably be banned to save the game and expand on the current metagame. Then (if Metaknight's ban doesn't solve anything), the only option for keeping the game alive will be a modded version of the game that adds depth and balance; i.e. Brawl+, Balanced Brawl.
Metaknight dittos are very common and no new mechanics have been discovered in the past year other than a couple subtle character-character matchup specific things. Metaknight has been and is banned at some tournaments, though not the big ones.
Some people actually like Brawl. Enough people like Brawl to want to play it in tournaments across the globe. I've talked to some of them and they seriously like Brawl more than Melee, consider Brawl+ an abomination to the game, and find Metaknight dittos exhilarating. Because of them, Brawl will not die in the short term.
Brawl+ is common enough to be a major player these days. It's no longer relegated to side-events. There really are 3 games now. But despite the growing popularity of B+ and the resurgence of Melee in the past year, one glance at the regional zones suggests that there are more tournaments for Brawl than there are for Brawl+ and Melee combined. As someone that expected competitive Brawl to evaporate by now, that astounds me. I think it may actually survive quite a while, at least until the next Smash Bros release. (There will definitely be another. The popularity of the last two was overwhelming, Nintendo would have to capitalize on that for their next console).
To summarize: Brawl+ will not replace Brawl. It has become a different game for a different group of people, and we're fortunate that enough people like Smash Bros to support 3 games for now.