I don't think this is a good idea for a few reasons. Could some local tournaments decide to run some unofficial patches? Sure. Anything larger than that and you run into a bunch of potential problems.
#1: Unwanted attention from Nintendo. As far as I know, they never did anything about Project M, but that doesn't mean they never will do anything. Seeing how they've cracked down on Let's Players it seems somewhat likely that they might not be too happy about mods either.
#2: Split community. Some will prefer the vanilla and some will prefer the unofficial patch.
#3: Perceived balance issues. Perhaps some characters will be considered overbuffed, or perhaps some other changes in the patch makes it controversial.
#4: Ease of getting into. Getting a mod to work is a lot more complicated than just booting a Smash 4 copy and playing. Not to mention that you'd have to manually update, while with official patches you can just download them through the Wii U.
Smash 4 is much more balanced than Brawl was, and is generally better received by the competitive community. There is much less demand for a "PM"-like project. The unofficial patch could help make more characters viable, but it's not strictly needed right now