nostr:nprofile1qqsdulkdrc5hdf4dktl6taxmsxnasykghdnf32sqmnc7w6km2hhav3g2kyjn9 has been working on DID support for Nostr, which would make any Nostr key pair pluggable into the DID/VC ecosystem.

I just read a blog post regarding the cost of moving social networks, and how Facebook integrated a "backdoor" into MySpace allowing users to migrate more easily back in the day. Mastodon did something similar when people started exit from Twitter, until they stopped it by closing down their APIs.

The bridge with Mastodon that nostr:nprofile1qqsqgc0uhmxycvm5gwvn944c7yfxnnxm0nyh8tt62zhrvtd3xkj8fhggpt7fy built works fairly well, it does increase the amount of content on Nostr.

You're pointing out a major issue though and there is no good solution to the situation.