It's a cliché at this point, but 4.0 (or more realistically, 4.1/4.2) would be the milestone that would result in professional adoption of Godot. 3D is still at indie-level now, and requires a lot of workarounds and hacks for some advanced stuff.
Even if you don’t go for godot as your main engine, the speed with which you can prototype is really nice.