My first thoughts on DLC were similar to yours: Bring back cut vets (top priority), and add clones. For example, one clone I'm sure many people would love is Lucina, from Fire Emblem Awakening. She could be a clone of Marth -- lighter, faster, hitting with multiple strikes -- but she'd be visually distinct with her flowing hair, etc. It'd be simple to design and would mean a lot to the fans.Making brand new characters like Inklings DLC sort of kills hype for an eventual Smash 5 though.
I feel like DLC characters should only go as far as bringing back cut characters and adding new clones (like Slippy as a new Fox clone)
So I think all of that would be great. But maybe Sakurai could throw us a 100% new character here and there, as well. Part of being a Nintendo fan is having fun imagining how Nintendo will play their various cards, and that part of me likes to picture a scenario where Sakurai adds the Inklings as a promotion for the release of Splatoon...