Been thinking about the topic of how post-launch free updates and DLC should be handled (controversial as that latter subject is, given the already steep price), especially since this'll probably replace MK8 and Tour as the game that's going to be milked for a decade+ before the ACTUAL "next MK"...
First off given all the content this game seems to have at launch, I think the dreaded "nintendo relies on free updates to finish the game" thing from the Switch era would actually work much better here since... this already looks like a "complete game" anyways. What said updates would entail, I don't know, it'd probably be things like more costumes and even more odd character additions that they couldn't fit into a DLC pack.
...Which brings me to my hope for how actual paid DLC should be handled. For one, they need to be beefy, gotta justify whatever price it has somehow. The wait between all them can be pretty long for all I care, they just need to feel "worth it" for me. I want both a bunch of characters and a substantial map expansion in each one.
But here's the fun thing I'm hoping for: I want the packs to be themed, mainly around specific Mario games. I think the Direct in a couple weeks will reveal the full roster of racers and courses (in the event of "oh surprise that's not the whole map!"), which might change my views and hopes, but say this game doesn't have a lot of characters from the Galaxy games, Odyssey, Wonder, etc. Well, why not have these huge packs themed around them? Make the map expansions add their distinct locales (or places that look close enough to them), and have character expansions that focus on that game's/series' side characters.
And if they come back to crossovers with other Nintendo franchises, treat them the same and go all the way as well. I don't want just Isabelle popping up in an otherwise Mario-themed pack again; if you're doing Animal Crossing, Zelda, Splatoon, etc., go the same route with them as this roster's doing and pull out all the stops with their side characters.
