This is a cool idea, are you thinking of self-hosting this or on their servers? Have they mentioned anything about any guidelines for what their blob storage can be used for? I know doom is small and that's a great idea, a workshop is a perfect example of how this can be used. I'm just wondering if this can be abused to outsource large server space.
Look into Lexicon on https://atproto.com
You can define custom records for basically anything
A PDS would be a point in the network that decides if abuse is happening, also a place where competition can occur