But it’s also based on “one major release per year”
No, that’s based on “release a major when we have something to release”. A major release is something huge, that gets special attention, even a dedicated announcement post. Maybe even some media coverage if we do it right (and I guess we can agree that this would be very much needed).
If we postpone the federation to 0.7.0.0 and, let’s say, we push that in fall. What do we have to show off? A new federation layer? Why should someone external even care? I doubt the chat will be polished and I doubt the API will be done in fall. So we’d have a major with… nothing interesting for external people. Not that nice.
If we bundle 0.6.0.0 with the federation, we have something to show off to external people (“look, everything looks fancy!”) and magically, the federation stability improves. Win-win!