I think the only way to avoid a CDDB is to make the entire database downloadable so that someone, or a group of someones, is able to re-create it in case of disaster.

I think in the case of "great, open service" selling, the new buyer can just change the licensing, and you're out of luck. If there is a license that compels them to maintain some level of availability, you can trust them to cut it down to the absolute minimum, including rate limiting access down to a level of pointlessness.

Yes, if I remember correctly it was one of the reasons the CC licenses were created? But I could be remembering wrong.

Yes, that is why the MetaBrainz Foundation was created - good luck “purchasing” the MusicBrainz database :)