Ehh, didn't Ridley have Samus Returns on the 3DS? I'm not sure, I don't keep up with Metroid, but my point is that Ridley's popularity may have led Sakurai to reconsider his status as a boss character. Waluigi's isn't likely to get Sakurai to reconsider him if he's never considered him in the first place.
Daisy still could use the moves just fine, and I don't think they'd feel tackled on at all. I could imagine her fighting using the dice, using a baseball bat, etc. She's a sporty, competitive, energetic gal, so her bringing her dice from Mario Party, her baseball bat from Sluggers, and a soccer ball from Strikers would tie into that very well.
It's true that DLC production hasn't started, but popularity alone still won't be enough for Waluigi to get into Smash. He has no importance to his series (so Ridley's situation can't apply to him) and Mario is still missing two very crucial characters (a Toad and Paper Mario, regardless of if you want him or not). There also is Geno to consider should Sakurai choose to add him. Waluigi has nothing to him to make him stand out against his competition.