Smash Kart - we are almost there already

Recently, there have been more and more crossover-titles, the most famous still is Smash Bros.

Somewhere I found a discussion, about whether Nintendo should make a crossover racing game, which was called there "Smash Kart".

I never played Diddy Kong Racing, so I cannot speak to the necessety of a sequel of this game, however I played and enoyed 1080° and Wave Race an N64 and NGC, but I am unsure if sequels could succeed in the current market. This probably is also, what Nintendo is thinking, because I do not even remember talks about possible sequels in the last years, if not decade.

But back to Smash Kart.
We more or less have it with Mario Kart.
While it is called Mario Kart, and in the first Mario Kart Game on the SNES there were only Mario, Luigi, Yoshi, Peach, Bowser, Donkey Kong, Koopa and Toad to choose as drivers, with Mario Kart 8 Deluxe were are almost there already.

A few characters might have started in Mario games, Wario and Donkey Kong most prominently, but they have not been in a core Mario game for quite some time.
Besides them we have drivers from completely different franchises: Splatoon, Animal Crossing, Zelda and the Miis.
We have tracks from different franchises: Again Animal Crossing and Zelda, but also Excite Bike and F-Zero, two other relevent Nintendo racing franchises.
And again with the cars: Besides the franchises already mentioned, we have a car named Steel Driver, which references Steel Diver.

Yes, Mario Kart is mostly Mario, but Smash Bros Ultimate is mostly Mario and Fire Emblem these days.

But I do like and support the idea of more crossovers in Mario Kart:

There are already tracks with snow, ice, water, beaches and such, so it would be easy to somehow incorporate 1080° and Wave Race.
Both Metroid and Star Fox could be made into cars based an Samus' ship and a Star Wing, like F-Zero's Blue Falcon.
Fire Emblem is a little trickier, because a FE-track would likely be similar to either the Hyrule track or Bowser's Castle.
Pokémon is still a sore spot for me, but could be done easily.
Ice Climbers was my first ever videogame, so I would love them as drivers or with their own track, but from Nintendo's point of view, there is not much reason to do so. Similar with many other, older franchises which are discontinued like Earth Bound  or Kid Icarus (or long time hibernating at best).
The most easy way to include a franchise is of course with the soundtrack, as Smash Bros shows.

And, if there will be no Diddy Kong Racing sequel, he at least should become a driver in Mario Kart 9.