Will Waluigi ever be in Smash Bros. Will he just get the middle finger saying **** OFF!?

Considering that Nintendo have always neglected him, probably not (he's never even appeared in a main Mario game!) If you wanna play as him in a Smash Bros game the closest you can probably get is in the fan-game, Super Smash Bros Crusade, which includes him and a bunch of other characters who never got to be in an official one.

I'm still hoping Bubsy Bobcat will be in Smash

I love playing as Luigi, so honestly I’d really like if they made just a skin. But yeah I wouldn’t expect more than that unless they’re committed to EVEN MORE CHARACTERS in the next one. 

I bet they wait until the next smash game so they can advertise that it finally has Waluigi to try to sell the game, which they might need to do since they have said they might not be able to bring back every character from Ultimate into the next one. If the next SSB is going to have less characters they will need to add a few characters with a lot of hype to compensate.