If you start thinking certain characters are “locks” you’re gonna have a baaaaad time. I think a lot of people are massively overstating the importance of certain aspects regarding their character getting including.
For example, everybody said "Ashley and Mimikyu are super popular and are really unique! They also (as of 8/08/18) haven't been shown as Assist Trophies, a Pokeball, or stage element!"
Some of us are now saying the same exact things about particular characters and now calling them "locks". Unless there's actually proof of each character being in the game, there's no reason to conclude they're in. I know everybody is excited (I sure as hell am). But you have to hype responsibly. Every Smash game, people come out and say, "YO. THERE'S NO WAY THEY'RE NOT ADDING X TO THE GAME"...guess what? They might not have added X to the game, lol.
Another thing about that...despite the amount of love he gets on this website and a few other sites, Bandanna Waddle Dee is absolutely not on par with Ridley or K.Rool in terms of popularity. Nobody is close. The only characters that have lasted long and were popular around the time that at least Ridley really started are Isaac, Geno, and maybe Skull Kid.
I can definitely say that people basically said there's no way Isaac and Geno wouldn't be added at one point. That obviously didn't work out. I'm going to go ahead and assume that people saying certain characters are "locks" are effectively just stating their confidence in certain characters getting in. That's fine. But I still think you're asking for it if you think more than a few characters are "locks".
If we follow Vergeben, the closest things to a "lock" right now would be Incineroar, Isabelle, and Ken. Those are probably the closest thing to a potential "lock".