I posted this in another thread, but it's also relevant here.
One of the reason's we've not fully released on Steam is because we're still integrating major features. When we work on something that's highly integrated into the rest of the code, like the base Physics engine and Collision systems. It will tend to stretch out the times between when we can release a stable version of the game. If there's even a small problem there, the game can be unplayable.
So, even if we've got features that are otherwise complete, we can't really release while the rest of the game is undergoing breaking changes.
We're actually looking into a different version control system, so we don't have these issues going forward where we have to wait on all features being complete before a release.