I'm hoping for (but not expecting) a complex tech tree, where you can add conditions like:
- Tech can be discovered, but requires Strategic Resource X in order to be researched.
- Tech will only work for photosynthetic species.
- Tech can only be discovered by a species with a weapons bonus above 5.
- Tech grants extra benefit X to lithovores.
- Tech is discovered upon defeating wandering monster X.
- Tech will be researched 10x faster if you have an outpost near a Black Hole.
- Tech can only be researched in zero G (requires research stations OR Anti-gravity research).
- Tech can only be researched if you secure access to Terran test subjects.
As I envision it, first you need to discover that a tech is possible. This has separate requirements: it's possible to invent lasers and perfect the "laser cannons" tech from them - and simply never realize that holograms are possible, even though you have all the requirements to build the tech. (This kind of knowledge is fairly easy to steal with a spy, or discover by chance if you interact a lot with a race.)
Discovery done, you need to research it. You know roughly what the requirements are. For example, you might need a huge particle accelerator, and so you have the option to invade Earth for a week - to make use of their CERN planetary installation - or to buddy up to the Terrans so you can rent lab-time there, or to give them the discovery and steal it from them once they've researched it.
Then, you make use of it - which is not guaranteed to work. If the Torians have researched Human Super-viagra, well it's not going to do THEM any good - but the Terrans will most assuredly pay big bucks for it.
Finally, there may be side-effects, bonuses and follow-up research. Maybe the Drengin turn out to be fatally allergic to the Super-viagra, and you can use it to poison their water supply during an invasion...
I think these kinds of things could really add some strategic aspects to the research part of the game. Of course, the REALLY difficult obstacles should be reserved for the very coolest, game-changing tech...