I think it would be fascinating if a few powerful abilities (see below) could be unlocked not by mastering ONE tech, but by (at least) TWO in two completely different branches of the tree.

For example, I would like to see some form of ability such as "Habitat Transplantation" or "Oxygen Dome" or whatever you want to call it be unlocked if, say, you research BOTH "Extreme Terraforming" and "Xeno Physics"; this ability will allow you to colonize "uninhabitable" planets with your colony modules and turn these planets into Class 4 planets when the colonists arrive.