Generally I would recommend just practicing some of the main beginner-friendly jumps/tricks like dino skip, moon skip, night metro awning jump and then focus on full runs at first. The general route isn't too difficult to learn especially if you have watched speedruns of the game (but it depends on each individual's experience). Once you know the route, practicing and improving general movement is the most important way to save time. Full game runs are great for that, but ILs can work too of course.

There are 33 timer challenges, according to the game/Toadette. https://pastebin.com/MsGTHVn0

Dark Side no revisits gets just over 124 moons by the end of Metro, it varies a bit depending on the route. If this would also end in Metro the route would probably be too similar, but if its faster to cut some more moons and add in Seaside (which would be very possible) it could be an interesting enough category to run.

Lake and Seaside could be interesting but the rest is virtually identical to any%. It reminds me of the suggestion of doing Sand kingdom without touching the sand. Maybe some more ideas like this could be combined to make a full run that is interesting with unique routing.

Considering Festival% was removed, and this would be the same but without Metro Kingdom, I'd say there is virtually no chance this would be added.

I doubt this will happen to be honest. Part of the problem is characterising what is an exploit and what isn't. For example, is moon skip an exploit? Personally I believe it was intended by nintendo but who knows. How about something like flower road skip in Wooded kingdom? It is simply a jump. Once you take out the clear exploits/glitches such as moon clip and fish clip in seaside the run wouldn't really be very different from any%.

I might try routing this and running it to see if its any fun.

There are no clips allowed in All Story Moons. World Peace is able to skip some story moons in sand and snow for example.

It just says 'There are no runs' when I check there after trying to submit.

Its not just you. I haven't been able to submit for 6 days now. Not sure how widespread the issue is but I have heard of a few affected by it.

I have the same problem, also for SMO any %.