Smash Ultimate's reception would have still been very positive thanks to all the returning veterans, I think. Newcomer hype would probably suffer, though. Now that we have Ridley and K. Rool, there aren't that many universally loved characters left; there are characters with niche followings, but nothing the size of those two. It seems like Geno, Isaac, and maaaaaaybe Bandana Dee are the only big crowd pleasers we have left that aren't third party, and sometimes I feel like maybe we overestimate how many people outside of the Smash fandom would get hyped for them.
All in all, if Smash Wii U had characters like K. Rool and Ridley, it would have been remembered a lot more fondly. Smash Ultimate's speculation probably wouldn't have as much hype going for it, but it would still be pretty close to what we have now: Regardless of them basically being locks, people like me were stoked for Inklings, and Konami fans would still be amazed by Simon and Richter. Not to mention Dark Samus making us Metroid fans even happier than we already were with Ridley, and Chrom being in due to popular demand. While I myself don't care for him too much, Ryu is a hype inclusion for a lot and would generate a lot of buzz if he were a newcomer for this game (just like he did back when he was DLC). Corrin probably would have been received even worse than they were back in 2016, as Fates and Corrin are suuuuuper hated nowadays and is kinda a punching bag game for the FE community. Cloud would have still blown people's minds like he did back on Wii U.
As for who the character to follow up K. Rool for the Direct? Hmm...I have a feeling it's not really gonna be a "hype" one per se, but more of an expected one. Probably a Pokemon, meaning whether or not it's hype for you depends on if you like Pokemon or not. While I do like Pokemon, I'm gonna be a little bummed if the next reveal is one from Gen 7, mainly because it feels really predictable to me. I'd be more interested if it was from an older gen, or maybe no new Pokemon at all and a focus on other franchises. That's just me, though; I know there are people here hoping for a new Pokemon from Gen 7.