Ahriman
Tyrant
I think its sensible to have a super-powerful end-game military tech so that you can finish up a Conquest win; the game is really dragging by that stage.There's no reason to believe it has to be true in a game that also includes GDR's.
Having said that, you have a fair point in that GDRs could fulfill that role at least as well as Nukes.
But it certainly feels very weird to be able to intercept a nuclear missile.
I guess it wouldn't be unreasonable to have a laser-defense building that required, say, Lasers and Satellites, or Particle Physics. But regular SAMs or AA guns or fighters? No way.
I dislike the idea of artificially preventing the AI from using nukes if it has them. I think you should be very afraid of nuke-wielding AIs in the late-game.
If people think nukes are too available I'd rather increase their cost (or cost of Manhatten Project) than to prevent a player from using them - particularly if they have nukes and you don't. What's the point of an AI building the Manhatten Project, acquiring Uranium, getting the nuclear techs and building up nukes (not exactly a low-cost combination) if they aren't pretty devastating?