It would be great to have a custom f-droid repo "alla guardianproject.info" (before getting git-annex into the main f-droid repo).
See https://github.com/guardianproject/fdroid-repo (https://guardianproject.info/repo/).
The f-droid developers are willing to add git-annex in principle, their build environment just needs to have its build dependencies added to it. I've completely automated (except for occasional breakage due to changes on hackage) to setup of the necessary cross build environment. I have not had time to look into how to integrate that into the f-droid build system, and it would be great if someone with interest could do so.
I suspect that setting up a custom f-droid repo would be just as much work, plus more work on an ongoing basis.
I've noticed that fdroidserver is available in the main debian repos, and not having really looked at it too much yet, if it shares similar code to wannabuild then it should be possible to continue everything as you're already doing it, just in addition rsync or git push the code base to a local fdroidserver instance and also copy the binary over once it's set up.
(if I understood wannabuild correctly, if you upload new source and a prebuilt binary it will mark that architecture as built.)
I opened a request to add git-annex in the F-Droid's submission queue about a year ago.
Just posting here the link, so that all the discussion (not much) can be found by those interested.
If I've understood Efraim correctly, he means that someone (perhaps, Joey) can run a custom F-Droid server with Joey's builds of the app copied to the repo as is (without rebuilding there), so that those using an F-Droid client would get the updates through this standard path (for them) instead of manually looking for updates here.
Like from a custom APT repository run not by Debian (in this case -- F-Droid team), but by an independent developer who is providing package builds not avaialble in Debian by building the packages himself, signing them, and putting them into his own APT repo (indexing them).