This.....this is exciting. Being able to basically CREATE your main is something that I love in sm4sh, and bringing that to the tourney scene will really spice things up.
I have a hard time understanding the arguements against it; mostly they just consist of "these are broken" or "the meta's going to revolve around this single custom/character that uses this custom," or even "this will only make top tiers better." To which I reply:
Firstly....it's not going to divide the roster, it's going to narrow the space between tiers. Even if top tier characters have solid customs, lower tier characters will have access to the ability to COUNTER those customs, as well as the top tier's default specials. Every custom has its weakness; regardless of how crippling that weakness is overall, there's always one particular character that can capitalize on that weakness. Not to mention, it's going to give otherwise poor characters a chance to really shine. Little Mac is downtrodden because of his poor recovery....making that better, even just a little bit, will really give him more of a chance. Counterpicks overall will become more interesting and requiring of creativity, as a single moveset change can turn a poor matchup into an equal or even an advantageous one.
As for overcentralization of certain moves and techniques...
>Ice Climbers' chain throws in melee/brawl
>Diddy's bananas in brawl, and his Hoo Haa in ssb4
>Brawl Meta Knight and his Up special
>And much, much more
There has always been, and always will always be that he character who's good because of "THAT ONE THING." It's the case for not only every iteration of smash, but fighting games in general.
With that long text wall finished.....I bid you adeu.