When it comes to potential Smash newcomers I'm usually one of two extremes: "put this character in Smash" and "keep this character as far away from Smash as possible." - there's rare cases where I'm indifferent, but you'd never find me having mixed feelings on a potential newcomer...
except with Tetromino
Let me get this clear: Tetromino deserves the spot, Tetromino has the moveset potential, Tetromino would be a really hype moment if it were revealed.
The problem is that I can't really envision Tetromino in Smash because I'm not sure what level of anthropomorphism it should be granted.
Should it squash, stretch, and bounce around like a
90s CGI advert? Should it move in a rigid but lively fashion like Steve? Should it just be treated as a lifeless inanimate object that's somehow moving a la the Iron Checkpoint Crate in CTR?
Whatever way Tetromino is animated would have such a huge effect on its moveset and while I have a preferance for the inanimate/lifeless option the other styles all have their advantages.
There's also the problem of deciding which shape should be treated as the default/idle animation, as well as the size/height of the Tetromino.
I'd love Tetromino to join the battle and think the Smash team could pull it off, but it's too much of a logistic nightmare to actively support.
If I were put in charge of a new Smash game, I'd probably only include Tetromino if I was mandated to exclusively include relevant and popular characters - and in that case I'd probably opt out of the project.