No it wouldn't. If an Assist Trophy was made playable, they would HAVE to make a new model from scratch, to account for size changes (which might be necessary for some characters to rebalance them), the lack of facial animation, they would have to build a new animation rig from scratch to account for all of the new animations the character will have, etc. The workload would be no different to adding a character from scratch. And don't try to defy me on that, because I have worked with 3D models quite a bit myself and games design in general, so I know the processes behind game's development. Examining these models up close and personal in 3D software, it's clear they were made for a specific purpose, and it wasn't playable fighter status. They would require new models.
I "will defy you" (lol) on that, because I work in the games industry and study 3D Modeling in college, and I'm having trouble believing your stories if you apparently don't even know how to touch up a 3D model.
Of course they'd have too edit the existing models, I'm not saying they wouldn't, but in the gaming industry you reuse assets whenever you can, it saves time and effort to do so. Ness was probably used as a base for Lucas, Roy will probably use Marth as a base, etc. The existing AT models are not good enough to be playable, but it would be easier to edit them then too make a new one.
Granted, the effort is negligible compared to the ridiculous amount of time it takes to do everything else too make the character, but it does take less effort
At that point, it's redundant for them to make them playable when they have their role in the game already, and they could be spending time putting MORE characters in the game.
So you think it would be redundant to do this. That's fine, I understand that, it's a perfectly valid opinion, I respect that.
Have you got any sort of proof at all that Sakurai shares your view?
DLC isn't something that's happened before, we do not know what his views and rules are in regards to it, there's no precedence for it.
I wish they'd spend time putting more characters in the game instead of assigning existing ones multiple roles, I'd replace
with ANY other Metroid character if that were the case.