They put so much work into Smash U ... it kinda makes sense to port it or take it a base and simply throw new content onto it.

I don't think a proper new Smash would be ready for this year otherwise.

Smash 4 sold 13 million units between the Wii U and the 3DS versions. It has had a big presence at 3 straight Evos and will probably be at Evo 2018 too. It's had a really nice run. Personally, I'm fine waiting for whatever a Smash 5 would be. But the odds of getting a Smash 5 on Switch go to zero in my estimation, if we get a Smash 4 port.

You'll get both I would assume. Switch is definitely getting a Mario Kart 9. 

Most people did not get a chance to play the Wii U version of Smash 4. 

I hope you're right, but they've never done more than one Mario Kart or more than one Smash on a system before. I wouldn't hold my breath.

I think the number of Smash fans who missed out on Smash 4 is much smaller than the number of Mario Kart fans who missed out on MK8.

MK8 and Smash 4 would be ports so this would still hold true even with a Mario Kart 9 and Smash 5 on Switch.

This is true but then again they never released a hybrid consoles until Switch so who knows.

Maybe it will be something like

2017-Mario Kart 8 Deluxe

2018-Smash Bros 4 Deluxe

2020-Mario Kart 9

2021-Smash Bros 5

Im really disappointed if true, call me greedy but i want a new smash, new 2d mario thats not new, new Luigi mansion, new mario maker, mario strikes, pikmin, animal crossing, wii sports, 2d zelda, all before e3 haha wantgames no

Is there need for MK9 in switch, when the Wii u port sells like a brand new Mario kart game ? I don't think so!
Let Nintendo save it for switch successor.

At this point I dont think we will have two Smash Bros games on Switch. MK9 is possible because MK8D was released only few months after Switch launch so there is plenty of time for another game.

Hmmm, well even so they would still need a 'flagship' game which, outside of Smash perhaps, ports can't really fill in for. Seeing that we are still getting new games (Yoshi/Kirby, Labo), and that last year, really, we did get a good amount of ports anyways (MK8, Pokken), i don't think it'll be all that different. We still know next to nothing about this year's offerings past like May, as well.

Can't blame them for being so willing to port though, after seeing the sales it would be refusing what is really instant profit.