Me and a couple of others did runs of this for fun a while ago, it was a fun category (I cant find my highlight but my time was 1:10:49) Also we timed by adding up all the times at the end of the track. Amber made a spreadsheet used to time https://docs.google.com/spreadsheets/d/17_8fAxW9bXKUcERjM7NFvewXF4_ZUe9XyfL2_RIVFFM/edit?copiedFromTrash#gid=0 . I wouldn't mind seeing this on the boards but its not a category I've seen on any other mario kart game. Also OP asking for a category and not supplying video or even a time to prove you've done a run is dumb.
The question always is, will people run it? For Shine Thief, which is definitely the most miscellaneous category on the leaderboard, the answer was “yes.” If you can really find several other people to do it with you, I don’t have too much of an issue with adding it.
However, I don’t think your proposal is original and unique enough to warrant another fracture in the body of runners. If you want to time trial with shrooms, then do it. There are already leaderboards dedicated exclusively to time-trials, including one in-game. If you just don’t want to deal with RNG, then run no items where the impact of RNG is extremely small.
That’s my personal opinion. Maybe some others will want to run it as well, but I’m all for keeping the number of categories as small as possible to boost competition and motivation. In my view, there are already enough sub-categories to satisfy everyone’s preferences.
