The problem with an approach like this (and it's been done before, usually on paid sites) is that there are many many more writers than there are agents or slots on agents' rosters. The supply vastly outweighs the demand. Honestly, I would much rather find agents who style I like and who are looking for what I want and put my work in front of them rather than put it out there and hope the agent I want stumbles across it.
Maybe this model would work if your thought process is "agent, any agent," rather than the best agent for my career.
I'm not against pitch parties. Sure, have a permanent hashtag to list available MS, but it doesn't beat the option to send an in-depth explanation of my work to an agent I want to work with. In other words, querying isn't as broken as you seem to think it is.
(Also, YA is a category, not a genre)