Ofcourse it wouldn't happen - but what the hell of the point of even mentioning putting characters in Brawl? I mean, come on. Dream a little, who cares if they don't stand a chance to get in.
Aaanyways.. About that Goku moveset before, I think I could refine those specials a bit.
Up B Instant Transmission: Instead of mimicing Sheik in every way, this move should be a lot like Mewtwo's, with a short amount of startup lag. As soon as he teleports, his line of movement shines in a jagged path. If anyone gets hit by it, he'll reappear with superarmor and deliver a doublehanded blow from above, which is a weak spike. Little damage, but the super armor means Goku's pretty much safe. The little distance can also be made up for.
If Goku does hit an enemy with the doublefist move, he'll use the instant transmission in rapid succession, letting you choose a new direction to move to. Very much like Pikachu's quick attack. However, if he doesn't grab a ledge, he's very vulneralbe, as he plummets at a very stiff angle. If you sweetspot the ledge though, you're completely safe.
Down B: The transformation idea isn't too bad, although I think only one form(SSJ1)should be available. As mentioned, all his attacks are stronger, his jumps are slightly higher, and he's slightly quicker, but his damage will rack up quickly. This can be used for super armor as well. Great for landing the killing blow or racking up damage quickly in the beginning. While the entire time you're gaining consistently good amounts of damage, if you hold it for over 25 seconds or so the damage you take will start to double, meaning you can't abuse this. If you rapidly transform on and off, the amount of time doesn't wear off either - you need to wait a short amount of time to make sure your "time limit" goes back to normal.
Side B: ..Yeah, Kamehameha, what'd you expect? There are a few possibilities for this. First, he can charge it like Samus' Charge Shot and keep it until he wants to use it, or he can quickly shout out, ..well, you know, and then fire the blast. For option one, it'd have impeccable range, and probably as much power as Samus' charge shot. It hits multiple times to rack up good damage, and the final shot has knockback. However, if you miss and your opponent manages to get behind you, you're probably screwed.
For option two with the instant shot, it'd come out probably as fast as Ike's F-smash, but again since it has a large range it's a great move. However, the move is a two-shotter. The first hit is like a gravitational pull, sucking the enemy in. Then the wave vanishes in a flash and knocks everyone flying. It'd have good damage and great knockback, but landing it is the main problem.
B: Ki-Blasts. Yeah, simple. If for Side B option 2 is used, this should probably be a charge up move. Instead of getting stronger when charged, you'll shoot multiple Ki blasts rapidly, one after another. Knockback isn't the priority here, as the blasts are swift and carryable, as well as a projectile. Damage can be above average, but the knockback is pretty average, maybe even below. Good launched speed too, probably around Link's Gale Boomerang speed.
His FS has quite a few possibilities. Vegeta could always sneak into the Brawl and perform their rediculously stupid but powerful fusion dance, transforming into Gogeta(no, not SSJ4). All the moves get powered up, ofcourse. Probably equal to a down B. However, his Down B can stack up on this FS, letting Gogeta for yes, SSJ4. Side B=Big Bang Kamehameha, anyone? :P
The transformation FS has tons of possibilities though, he could go 3, and use his Down B to go even 4. Whichever you prefer, really.
As for a non-transformation FS, there's again, tons of possibilities. Classic Spirit Bomb, temp. transform/fusion to whip out some really awesome move, too many ideas that I'm going to get into.
Anyways.. I modified this moveset from pharos' on the spot, but I think it's passable, yeah?