I really want for Steve to get into Smash, but that is honestly because of my own severe bias as he really is a pretty crummy character choice.
I've played Minecraft for years - since about 2011 (Beta 1.8) - before Minecraft had the reputation of being a cringefest for 11-year-olds (Although in retrospect I wasn't much better than that at the time). I remember reading practically every article in the Minecraft wiki, though nowadays I've fallen behind. I can remember when I read the old article, "Player," and how it described the player as having no official name. The closest he got to an independent character at the time was a half-acknowledgement as "Steve?," with a very intentional question mark. The point was that "Steve" wasn't a character - YOU were the player, and the game was yours. Eventually the question mark stopped showing up around the time when the secondary "Alex" character model was introduced, officializing the two identities. But what this goes to show for me is that I don't really care so much about Steve as Steve. Steve is really lacking as his own character - I mean, half the time you hear someone bring him up without preestablished context he has to be explicitly referred to as "Minecraft Steve" because he isn't the icon. Minecraft itself is, with its blocks and Creepers and such. So when I say that I want Steve as a character, what I am really feeling is a desire for what is probably my favorite game of all time to be recognized by what will likely be my second favorite game of all time; and not just with an extra stage, but with the highest honor that Smash has - a character.
That being said, I do think that a stage is far and away the best way Minecraft could be represented. Not only is Steve not Minecraft's icon, but I can't imagine Steve appearing and being animated well as a playable fighter. (I doubt it will be that bad if we actually end up seeing him, though.) As far as stage picks go, the best choice visually would be "Overworld," but I also think that "The End" would probably be the best for layout and function. (Also, fingers crossed that the stage would have a competitive layout! I would pay $30 for DLC of that quality!) What I'm really wondering about is music - Minecraft has a killer soundtrack for Minecraft, but for Smash? I have C418's albums on iTunes, but I can't think of a single track that would be exciting to smash to. I guess it would be interesting to see what happens.
Honestly I'm just afraid that I'm getting my hopes up too much. While at this point I feel rather confident in the Minecraft content leaks, I don't think that I could help but feel a little bit let down if Minecraft couldn't get in character-and-all. I guess that is just the nature of Smash speculation, though.