Here's another question for ya'll:
What's your pipe dream character? That is, a character which is technically eligible but it likely won't happen for one reason or another?
For me, that's a character from Wizard101, an MMO I play alot. It's technically eligable but A) It's an MMO which has had nothing ever representing that genre and B) The game is already long past it's prime and I don't think it's likely to be even considered ever.
On the odd chance it does happen ever I would love to see some of Wiz's ost; it's some really banger stuff, like this track:
Maybe even some Pirate101 ost but that's pushing it I wager.
Brian from Quest 64.
It's not simply cause the Quest franchise is currently dead(I can't say finished, since they did scrap the sequel, titled Quest 64 2 at the time), it's because it's also 3rd party and Nintendo would have no reason to license something they can't make money off of. If it's at least an active product, it's not a big deal if they don't outright make money beyond the sales. Like with Banjo-Kazooie, where Microsoft is clearly getting the advertisements. It doesn't have this luxury. And there's no reason to buy the rights to it, since there's no guarantee it'd sell well, even if they released it via some collection on the Switch.
It's not a matter of unique gameplay Brian could bring or anything like that. There's multiple ways to make it work. You don't even need an MP meter, which admittedly is too difficult to balance when a spell costs 1, 2, or 3 points to cast(and if they included boss spells, theoretically 4). Being a master of 4 elements, there's tons of options for filling out moves alone.
That said, Quest's OST is lovely, even as midis alone. It has a ton of unique enemy designs that make for very easy spirits. The hardest thing is figuring out a stage at best, since finding a location that's iconic to the series isn't too easy, but moreso on what kind of mechanics the stage could have to make it actually interesting. It's notable enough that the only hack was just a remake of Green Greens with different colors alone representing World of Mammon. And there's more than one stage that could be loosely used(Pokemon Stadium 2 can easily show off some of the various game areas. Like the Flying section could be turned into Normoon) for a hack alone. I even had trouble figuring out something good, before going with Isle of Skye(using Blue Cave and Crystal Valley as part of it) just to make a fun and interesting stage.
The last thing is it not having a good chance to sell well as DLC. Not even as a bonus character(not that Quest lacks a fanbase, but it clearly was not one of the better selling franchises to begin with). He'd work fine as a base game addition, since there's multiple other more notable characters anyway to want.