I wanted to post in here in support for this category as someone who is interested in running this game, though obviously I trust mod judgement on the category.
I would also think its nearly guaranteed to be a thing, especially with the experience boost that having a second player grants if you can be consistent with synchronized throwing.
The caveat with second player would be when are they allowed, as while they are fine in large field maps and gyms, they are not so useful when you need to transition between several screens in rapid succession. I would permit swap in only for that reason, as knowing when to tag in P2 and when to leave them out becomes part of the challenge.
Would probably label the category as any% (support trainer allowed) because 2p2c probably would fall in the same amount of difficulty.