One research token for 5IPC after you capture a victory city. This biases towards the axis, but I’m thinking that that can be a good thing in this game. One roll each turn. When you hit a six, you roll again to pick which branch (odds = 1, evens = 2). Then you roll for the tech. Variations on this might work.
Maybe, to make it fairer, there is just one tech per power, but it can’t be placed in their capital unless they only have one victory city. China has no tech, but ANZAC do, because we invented the photocopier and the multiple beer tap. For example, Japan might get a tech token if it takes Hong Kong, but not India. Italy gets one if it takes Cairo. Germany gets one if it take one of the Russian cities that the Russian player declared includes a tech token. Russia gets one if it takes Warsaw and the US get one if it takes Rome. That sort of thing. US would probably need to put one in Hawaii which could prompt Japan to attack earlier, to their detriment… but they will eventually get a tech (probably -maybe not).
The nations were constantly collecting foreign scientists for their own efforts.