Well if you read my initial post, I mention that it really does seem impossible. I think the bigger draw to these characters is better described in my initial post about the subject, though. It was/is a revolutionary game, and is from a company that has published games with Nintendo in the past. And as far as third parties go, we have characters that are iconic from their own regions of gaming. RPGs with Cloud, Platformers with Sonic, Fighters with Ryu, and then Pac Man just being who he is to gaming. WoW/Warcraft would fall into a completely separate category, covering both the huge MMO genre, as well as RTS genre as the characters overlap. Now I think the concept is next to impossible, but I also think that characters from that universe check the boxes of being a third party character, the only argument being appearing on Nintendo consoles, which isn't really true due to Cloud.
Now in regards to the post you quoted, I think it could move a decent amount more consoles, and maybe even more copies of the game too. I know a lot of people who own a Switch to play RPGs like Xenoblade Chronicles 2 and Breath of the Wild, but they don't intend to buy Smash. If you implemented a character from Warcraft, though, many of them would be far more interested in buying it. So many people recognize Warcraft characters and it would actually reach a new crowd. I think the size of that crowd is being a little underestimated by you as many of those people wouldn't bother talking in a place like Smashboards to let everyone know they exist.
But, anyways, I was really just establishing the concept rather than calling it "likely" by any means, because it's not. I'd rank it in the >1% chance region for a Rate their Chances situation. That game has so many characters, and with the Alliance/Horde divide that is heavily present in WoW, you could make half of the fans wildly excited and half of the fans wildly upset that their faction isn't the one represented. In my experience with WoW, people are pretty loyal to their faction.
