In my opinion the current subtree format is getting outdated. Some new nations would really mess up the game. Since I don’t think they would add “Regional Subtrees”, I came up with a sketch.
Indian Su-30MKI, Rafale, Mirage 2000, MiG-29… all that in the British tech tree is actually insane.
Ukrainian F-16s, M2000s and MAYBE Gripens in the future…? That in the USSR tech tree is actually insane
Where would South Korea go? South American countries, Eastern European countries etc etc etc, where would all that go?
There are so many unique modifications or domestic projects that simply wouldn’t fit in the current subtree format. While talking about this with some friends a while ago I came up with a sketch. I used Ukraine as an easy example mainly to show how it would work.
Instead of being entirely separate nations or having a branch in an existing nation and calling it a “subtree”, add them as a TRUE subtree, a tab you click and get to start your research. Depending on what the earliest vehicles we could get from the subtree, I guess we could have a system similar to helicopters, where we have to play until a certain rank to unlock it.

I guess that would be Rank VI for Ukraine…? So play USSR up to rank V-VI and unlock the new subtree. There we can have some different modifications/versions of vehicles, some could be copypaste, but in Ukraine’s case it would be extremely fun to have Su-25s armed with Hammers or Flankers shooting HARMs etc etc.
I guess if an Indian subtree looked like this then yes, we could have the Su-30, MiG-29, Rafale, M2K and their own domestic projects all in the same place lol. Iran has F-4s and F-5s… but also has MiG-29s, Su-24s and Su-35s soon maybe, can’t have that in the US tree and we also can’t just spread their vehicles all around other tech trees.
TLDR I guess… Some new nations wouldn’t fit as standalone tech trees as they’re not big enough, some currently use or used a great variety of vehicles from different countries, so we can’t have something like F-16s in the USSR or Su-30s in GB… Solution? Add TRUE subtrees, not just one line of research in a tech tree and call it a day.