I'm in no hurry to let go of Mario Kart 8D, but I can't wait to see the next game!
I find Mario Kart 8 almost perfect gameplay-wise and it has the best track selection (nitro and retro) of any Mario Kart imo but new gameplay, new artistic direction and, more generally, new ideas will be much appreciated after so many years.
I'm not a big fan of City tracks either, my favorite is Amsterdam and it's precisely the one that feels the least "city", otherwise I'd say it's Sydney. I don't find most of them very inspired, that they lack memorable sections, and that they're pretty confusing the first time. That said, I don't hate them either, and I still enjoy playing them. And the three to come look very promising judged from the images I've seen, maybe my new top 3 will be all here