This actually has floated around the office in the past a few times. At the time the team even reached out to several individuals to test if this concept would be feasible.
The main issue is in the amount in tweaks, feedback and iterations needed to get any asset production ready.
Particularly so for 3D models which have quite a few technical requirements before being suitable for AO.
In the end, it wasn't really saving us much time due to the overhead involved.
These issues largely stem from being unable to provide volunteers with a pipeline to export and test their assets on their own.
And unfortunately, due to the way AO tools and assets work, it's not very feasible to provide these tools.
It would be awesome, but in practice without a good way for volunteers to test their assets, I don't see it working at least.
A community made model exporter (from AO to some common format) would go a long way for at least texture artists to be able to get work in a productive manner.