Smash 4 is a moneymaker, but it won't be a moneymaker 3 years from now. Nintendo needs as many moneymaker games. Nintendo can't afford to have another console flat bomb like the Wii U.
You can make Smash 4 a moneymaker for a solid year (especially with some DLC), but nothing more.
Ultimately what people want is:
1. Smash 4 on a console that more than just a few million people own and that isn't desperately underpowered in an underpowered console generation.
2. A new and current Smash game that fully realizes the technology of the system it is on.
Smash makes too much money to not have a remastered edition of the latest game and a new game, just like Mario Kart.
Remastering Smash 4 and developing Smash 5 is a lot less than making Smash 3DS and Smash Wii U at the same time and forcing the gameplay to be 1:1 on both.
Smash and Mario Kart are totally different games though. Each with their own specific development requirements. No one in Mario Kart has a unique moveset, or Final Smash. Unique speed variations and Kart/Motorcycle tricks are unique. That's it. It's a racing game.
For Smash, albeit clones, every character has their own unique moveset which takes a lot of time to formulate and implement. Then they have to balance all the characters, and create stages, and there's things like stage hazards, items, trophies, licensing for 3rd party characters, and so much more that goes into the development of that game.
For a Super Smash Bros 4 port with new characters/stages from the start, with new DLC coming down the pipeline, and it's visuals being slightly upgraded by Switch, AND Smash 5 to both be released for the Switch during it's lifetime is just not going to happen.
Development for Wii U/3DS ended back in early 2016 with Bayonetta's inclusion. That was only a year ago. If a Deluxe Smash 4 port that's a combination of Wii U/ 3DS features with new content is released along with the promise of DLC over the Switch's lifetime that will be THE Super Smash Bros Game for the Switch, and we won't see Smash 5 until the Switch's successor. Console lifespans won't allow for two Smash games to be on the same console because of the extreme amount of preparation and development that goes into them.
With Masahiro Sakurai himself saying he is tired of working on Super Smash Bros, I think it'll be a long time before we see an entirely new Smash. A Smash Port could come out Holiday/Sometime next year. Unless Smash 5 has some MAJOR cuts and less content, but I think we all know that a new Smash means new fighters, new stages, new items, and all that jazz. Sakurai has stated before that while cuts are necessary, he hates making them.
I even have to retract a statement I previously said. Smash for Wii U/3DS came out in late 2014, and was supported until early 2016. Technically, the game wasn't complete until 2016. We'll either get A Smash for Switch deluxe port, or Smash 5 in 3-4 years at the earliest, and that's with major cuts made to the roster and less content being added in.
It makes more since to get A port of Smash 4 out and support over YEARS with DLC to keep it fresh, exciting, and in people's mind. When I say this I mean A new character or two + new stage, every four months over the next 4 years. That'd be atleast 12 new characters and 12 new stages (which is wishful thinking really). That'd basically be a "new" Smash game and it'd be solely for the Switch. It be a port in essence alone, and would become its own definitive version of a Super Smash Bros game for the Switch.
With it taking 6-7 years between new Smash iterations, if we get a port, we won't see Smash 5 until the Switch's successor which is years and years from now. With all this being said, I can totally see them developing Smash 5 whilst supporting the port with DLC. By that I mean, DLC is a much lesser task than creating a new game from the ground up. It'd give Sakurai a chance to work on other things, develop a character every few months on the side, and then at some point a few years from now starting development on Smash 5 and having it ready for the Switch's successor in it's first year.
I'm sorry I can't see two Smash games on one console. It just seems insurmountably impossible to accomplish.