This transition will happen organically once ATproto exits the federation sandbox and goes live. I don't think the Bluesky team should try to force any specific BGS implementation on a community. There will be many BGS servers and even more AppView servers, each experimenting with different monetization strategies and moderation approaches. The market will decide which ones survive. 

Bluesky
Federation Architecture Overview - Bluesky
Soon, we’re launching a sandbox environment for federation. In advance, we want to share some technical details about our design decisions.