^I agree, getting locked out of late-game techs sounds awful. Unlocking those techs and then using the new toys is the best part of the game.
I'm going to hack the tech tree if it comes to that point.
A compromise could be made. I'm not familiar with the tech or its prerequisites, but what if you made all the options available, but harder to research for each consecutive discipline already unlocked?
Example: You research option 3, which takes Y time. Now you research option 1 which takes Y x2 time. Option 4 would take Y x3 and option 3 would take Y x4 time (the order wouldn't matter, only how many of the options that were already unlocked).
I dunno whether or not it's possble to dynamically alter a research topic's time cost ingame on the fly, or if you would have to have hidden duplicate topics for each possible situation.
Example: Option 1A with Y cost is available if no options has been researched yet. Option 1B with cost Y x2 is available if one of the other options has been researched, etc.