[Mark Walton]

I think there may be better ways to change the tech tree in such a way that research helps define the race.

The way I would go, is increase the breadth and depth of the tree, and add more leaves, so that no one player can research everything in a typical game.

Another non-hardcode way to implement something like you suggested, is to have more "theoretical" research items which exist only to open up a branch of the tech tree, and to make these all very expensive in Research Points.

Another-nother way might be to do something like, make these theoretical techs into ruins techs, and dot more ruins about.

Personally I don't like all the extra effort involved in your method, it just seems to limit players for very little gameplay benefit.