Ok, so the best Argument you guys have are:
"he's Popular"
and
"he should be in to complete the 4"
Ok.
1st: Yes, he is popular, everybody knows him, and 85% of that everybody hates him.
If he was too popular, he would have his own game, i mean, Wario has his own games, and Waluigi doesn't appear in them. Why? not even Nintendo likes him.
If he's in the party games, it's because in some of the minigames, the characters must team together, that's why Waluigi was created, and that's his only purpose.
Other than teaming with Wario on some minigames, he has no other purpose.
2nd:
No, he Shouldn't be in, only for that reason. If that's a valid reason, then Pico, Goroh and Dr. Stewart would be in Brawl with Falcon. So no.
Now, from my limited experience in the Smash Games, Sakurai likes to add weird chars, so he has a VERY SLIM chance of getting in, that's it, only that, if he whants to add some weird character and have 7 mario characters...
But i don't think he would do it, why? he whant's to add around 40 chars, all the characters he has announced are worthy characters, so far there are around 6 Mario characters, so why add waluigi, and take one spot from the roster?
When other worthy chars could have that Spot? Also, is not only the franchises that are already in Brawl, but others that deserve or should make an appareance, Golden Sun for example, we already see that new franchises are heading to BRawl, with the Animal Crossin stuff.
So unless Sakurai, whants to add another Mario character and a WTF char, then Waluigi whont be in, i mean, there are more worthy Mario chars out there like Bowser Jr.
. Plus other people have better arguments for Waluigi's inclusion than me. *Looks at Red_Maniac*