Seed migration (including a front-end) and a working API are two big steps towards a version 220.127.116.11! See this discussion: Requirements for a 1.x.y.z release.
@HankG, the policy so far, since diaspora* has been a community-run project, is to release a major version once there is a sufficient number of changes (or even one huge change). Your list is, I think, too conservative; two or three of the more major changes in your list would merit a major release on their own.
All of the things you list will be valuable additions, but I think you’ve got 3 major versions in your list. It would be a bad thing, I think, to hold up the release of seed migration, your API or post editing because of one other feature that no one has started. Any of those three features should be released as soon as they are ready,* because they’re all ones that the community has been crying out for.
*Of course, if there is another feature that is almost ready, we could wait for a short while so that can also be included in the release; but a release shouldn’t be held up unreasonably.
I would say a ‘blocker’ should be restricted to something that (a) absolutely has to be included as soon as possible; (b) needs to be included in order for something else being released to work properly; or (c) fixes a regression and would normally be included in a minor release. If the pace of development picks up from that in the past few years, major releases would become more frequent as more features and other major changes are made more quickly, so anything missing out on one major release would not necessarily have to wait many more months to be released.