I was thinking today that there actually might be a way that the core blockchain could get past the need for keys to the account to create the new posts:

1. Create a new "special account" like @null or @steem.dao
2. Use that account to create new posts when an account receives votes after 7 days with 100% beneficiary set to the original author.
3. Create something like a "pass through vote" operation that forwards votes from the original post to the new one.
   • The potential stumbling block in this step is that it might be difficult to find the new post from the old one - without scanning the entire blockchain or adding a reply to the original post. I suppose the new post could even be the reply, but that starts to look kludgy.
4. Provide updated API calls that deliver merged information from the original posts and all follow-on posts.

This doesn't change the fact that I'm pretty sure there's nobody who can work on this for the foreseeable future - and it slips away from the "you own your data" model, but it might not be as technically intractable as I had imagined.