This is pretty much my stance on the subject
He can certainly have a functioning/unique moveset, Legacy XP and SSF2 already did that.
But still, you'd have to pull off a whole list of C and D-listers aka literal scraps in order to make a cohesive spirit board. Say what you want, but all of them include very important characters and aspects from their respective franchises (XC2 has Rex, Minecraft has Ender Dragon, FF7 has Tifa and co., Tekken has Heihachi and Jin, Banjo has Gruntilda, etc.). Not to mention that spin-offs aren't exactly lacking in content either, we just got the party dice, tennis spirits and lots of stuff like the karts and MK songs.
Whatever they include, I don't really think it will be meaningful enough. Not to say he can't get in by any means, just food for thought. Personally, I think he'll be used as the selling point for Smash 6.