Some things to do with the P2P protocol are works in progress, needing a future flag day to complete.

VERSION over tor

Old versions of git-annex, before 6.20180312, which speak the P2P protocol over tor, don't support VERSION, and attempting to negotiate a version will cause the server to hang up the connection. To deal with this historical bug, the version is not currently negotiated when using the protocol over tor. At some point in the future, when all peers can be assumed to be upgraded, this should be changed.

git-annex-shell fallbacks

When using git-annex-shell p2pio, git-annex assumes that if it exits 1, it does not support that, and falls back to the old sendkey/rerecvkey, etc.

At some point in the future, once all git-annex and git-annex-shell can be assumed to be upgraded to 6.20180312, this fallback can be removed. It will allows removing a lot of code from git-annex-shell and a lot of fallback code from Remote.Git.