I like the idea of having more techs, but please include some level of automatic visibility. Like a number and/or a color for researchable techs that are behind that layer. Or even a number / color for techs are not ahead of time. I suggest this because I can be a very visual person, forgetting something if I don't get visually reminded of it. Thus it would be likely I would forget that I wasn't happening to be researching whatever was in that layer.
I'm enjoying the bit of letting my head run wild, with dividing up techs into offensive and defensive or whatever. Or even each branch of the tactics could have it own, such that germany could have a mobility window all to itself, allowing for way more room without the risk of the player missing something. Then, within that tree, which is the buttons, there would be more room for more branches on that tree.
Imagine if for land doctrines, instead of the 1 2 3 4 of the original post, it was a shield for defensive, a half track for mobility, a soldier for manpower, etc. Within defensive, you could have more branches between the british, french, italian nuances and ideosyncracies.
Its just example thoughts, but allowing for modable images for the layers and modable layers would open up the tech options a ton. I would be worried about a player not having everything instantly visible, as to me atleast good UI design requires that. It could be done with a color bar, reusing the standard colors for completed tech, available tech, unavailable tech. Thus, as the player completed tech and the game went on, the color bar would change from say 20% complete, 10% availible, 70% uncompleted to 70% completed, 10% available, 20 % uncompleted. I would think that would be a nice dopamine for players.
) image to show it:
