My two cents on Steve, as someone who doesn't play Minecraft:
Can Sakurai sell this character to people who don't play Minecraft? I've never played any of Simon Belmont's games before his reveal, and I was skeptical leading up to his announcement that he would be a good fit for Smash's third party choices. The trailer completely destroyed any concerns I had with the character and got me excited as hell for his inclusion in the game, and I instantly played the Classicvanias. Many years ago, Snake's inclusion did the same thing. Can Sakurai do that with Steve? Or is Steve the kind of character that only Minecraft fans really like?
If you're gonna add a third party, I think it should be a character with a broad appeal. Minecraft fans like Steve, and there's a lot of Minecraft fans, but how many of those overlap with the Smash userbase? And how can Steve be presented in a way to get people who have never touched Minecraft excited?
You can talk about the game's popularity and success until the cows come home, but we play as characters, not corporate stand-ins. While it's naive to think a game like Smash isn't littered with corporate mascots that help push software, Steve would feel the most transparent of these by far.
"Deserves" or not, as a complete outsider to Minecraft, nothing about Steve excites me. If he gets in, and I think he might, the world won't end, it'll just be another character out of 70+ that I don't care for. Spilled milk in the big scheme of things.