Ashley:
1) "WarioWare doesn't need any more reps. It's not big enough"
By that logic, Xenoblade doesn't need a second rep, either. It's a newer series comprised of three games, only one of which (XB2) actually managed to cross the "million-plus sales" threshold. WarioWare, as a series, has been around since the GBA/GameCube, and has had eight installments, three of which (Mega Microgames, Touched, Smooth Moves) have sold over a million copies (with its newest installment, WarioWare Gold, well on its way to be the fourth).
(By the way, this isn't me ragging on Xenoblade. I love Xenoblade 2, and I'd love to see Rex/Pyra in Smash, as would many others. I'm just trying to put things into perspective.)
2) "Ashley isn't an important enough character."
What constitutes as an important character, exactly? Within the confines of the WarioWare series, every character is about as important as the last (Wario excluded), so it really comes down to popularity. And sure, people might downplay the Mii Costume, cameo in Mario Maker, starring role in the Badge Arcade, three 3DS themes, and use in smaller-scale advertisements for eShop games/ a regional convenience store, as far as reasoning for promotion within Smash goes, but it is far more than any other WarioWare character has gotten.
3) "What could she even do?"
About as much as Captain Falcon does in F-Zero, I would presume.
No, but seriously. Ashley has been shown shooting stars with her wand, brewing potions, summoning plant monsters, riding brooms, shooting lightning out of her fingers Darth Sidious-style, unleashing an explosion of magic, and her best friend is an imp who can transform into just about anything she wants (including a pretty cool looking magic wand/scepter). If that isn't foundation enough for a moveset, then I'm not entirely sure what is.
Isabelle:
1) "She's a pacifist."
She's an Animal Crossing character. What character from that series
isn't a pacifist?
Waluigi:
1) "You only want him because he's a meme."
Actually, I've liked Waluigi since I was a child who knew very little about the Internet. I always thought his weird movements and petty personality were hilarious, and that few characters - if any - could effectively capture that same "two parts wacky, one part defeatist" aura that he gives off. Plus, he can swim in midair. That's such a weird concept and I love it. And so what if he's a meme? Obviously, he's such a ridiculous character that his antics resonate with a lot of people. How is that a bad thing? Be grateful we aren't talking about Shrek or Spongebob, haha.
2) "Some people on Twitter harassed Sakurai so I hope Sakurai punishes all Waluigi fans by never putting him in Smash Bros."
Before you pre-maturely bring down the hammer of justice on a large group of people, let's remember that that was only
some people.
SOME. I'm sure there were a few bad eggs in the Ridley, King K. Rool, Geno, etc. fandoms who said a nasty thing or two about Sakurai throughout the years. Are you willing to apply your personal sense of video game justice to those fans, as well, or is it just easier to feel that way about Waluigi because the timing is convenient?
3) "Waluigi isn't an important character."
In a franchise as simple as Mario, all it takes to be considered "important" is to show up, and Waluigi has done that in almost every Mario spin-off game since the N64. He shows up in merchandising the world over and
obviously has his fans, so...you're wrong.