I like it. The high level UX of this idea feels very compelling to me as a "yes and" -- aka a world where vendors continue to offer end-to-end encrypted syncin

I like it. The high level UX of this idea feels very compelling to me as a "yes and" -- aka a world where vendors continue to offer end-to-end encrypted syncing within an ecosystem, but then this idea gets layered on to solve the cross-ecosystem problem. I think the trickiest part would be how to do it in a privacy-preserving way, but that's solvable.