Basically, what about a category where you collect every unique invisible coin in the game at least once?

That category would take speedrunners in places where they don't usually go.

Or you can go even further and make a category where you collect every unique non-enemy coin in the game at least once. This means coins lying around, invisible coins, coin block coins (I wonder how multicoin blocks would count? Exhausting those blocks perhaps), coins from objects, coin rings, and coin piles.

That would be rather long category but at least there's no grinding.

I wonder what would be the main route differences in here compared to other categories.

tell me where all the coins are right now

Would these be longer categories than all missions?