I don't understand how people can't be excited for this... Like, I literally loved the game so much that I could even say I liked it more than MK, at least when I was little... 

I would be extremely happy if this was true.

Mario Kart 8 is old, it came out 6 years ago.

Mario Kart 8 is a Wii U game, it was designed around the Wii U's various hardware nuances, it isn't putting the Switchs 3x extra Ram, double the memory bandwidth, increased geometry, texturing and shader and streaming capabilities to full use.

Mario Kart 9 can take things allot further on the visuals front.

Uhh...I know how old 8 is. Which is why I said "I'd love a new Kart, who wouldn't at this point". Yes, it's obvious it's an old game but the fact remains that it's still selling like a new game. 

My guess would be:

"Excite" (Bike/Truck) Series

Thats fine as a smaller support title but it wouldnt be "the major holiday title" like the rumor suggests.

Doesn't help that the game gets bundled heavily as well.

Either way, I think a new entry could be fitting, Mario Kart 8 has shifted 22.96 million copies across WiiU and Switch (Granted there is some double dipping in that number, but who gives a shit.)
That is 22.96 million~ potential customers that a Mario Kart 9 could be very tempting for, so while yes... Mario Kart 8 is still selling, still priced high, Mario Kart 8 could help shift more consoles like it did for the WiiU.

Super underrated in the sense that it got massively overshadowed by Mario Kart. I would say MK64 was a little better overall but I loved the single player campaign in DKR and the fact that you could choose between 3 different types of vehicles. 

Brand new online DKR for Switch would be epic

Let me clarify. We already have a Mario Kart title on Switch, so another Mario Kart isn't going to move the needle. F-Zero offers something the Switch does have and can offer a difference experience. It can also be used in conjunction with their online. Not even saying they can't have both. They could easily outsource it to another studio which is what they did with F-Zero GX. Then you'd have your cake and eat it too. Comparing to Mario Kart was probably a bad idea. Nonetheless, it's silly they haven't had another one.

It actually sold 22.96M on Switch alone. With a further 8.5M on WiiU give or take.

First off, I want to say that I agree that a Mario Kart sequel is probably not on the horizon, but I think some of your reasoning is flawed.

You ask why they haven't released multiple Mario Karts every generation... I would suggest that it's because they take time to develop, and overly saturating the market with sequels tends to cause the IP's value to depreciate. But since Mario Kart 8 was a port, that means that it has been quite enough time for them to have developed a sequel by now.

You also say that it makes no business sense for them to cannibalize their best selling game with a sequel on the same system, which they've never done. It affects your credibility when you state things without verifying them first. Wii Sports and Wii Fit both had sequels on the same system. And I understand Wii Sports was a pack-in title, but the point is that just because a game is the "best-selling game on a console" doesn't mean it shouldn't get a sequel. In fact, I think most companies would be opportunistic and see great sales as a reason to make a sequel in the first place. Halo led to Halo 2. GTA3 led to Vice City. It's fairly common to make a sequel if sales are high. That's the thing about business.

Anyways, yeah, I doubt Nintendo will release another Mario Kart game on the Switch, although since I owned MK8 on both Wii U and on Switch, I am longing for a new MK experience myself. So for you to say, and I quote, "Nobody wants this"... it makes me wonder how you view the world.