Road to 56 plays with the tech tree, obviously expanding it (to 56), but also adds some extra doctrinal elements.
It doesn't seem likely they'll revisit it anytime soon, but it's also something that could really help add some strategy back to the game - I recall the HOI3 system of having way too many choices and being limited into what you could actually research, I'd kind of like to see if that system would work here (unlike now, where generally your build is the same for every game, unless you need a navy).