Y'know if HWL can get all these extra characters and content I don't see why not Smash NX can do the same thing. I even had an idea where instead of making a brand new Smash Bros game, Smash NX (which is ported from Smash Wii U) is released at launch with several new characters, stages, modes, etc and then every year a Character Pack, Stage Pack, and Misc Pack comes out towards the holiday season containing other characters/stages/other content to keep the game running all through the NX's lifecycle. It's a lot more practical than making a brand new Smash Bros game from scratch (having to cut several characters from the game) and characters requested by the fans have a much better chance of getting in the game.
As for who I want to see in HWL...
Any ALTTP character because that game is lacking in any representation in the game
Minish Cap Representation (Vaati)
Groose (Let him loose Nintendo)
Saria (Because she's a natural fit for the game and it's odd that she was omitted from the game)
Wolf Link & Midna (Makes sense given TP HD is a very recent thing)