How much you can demand should depend on how seriously you are beating them, though.
I mean, if they have one city left and you have a massive empire, them doing research at your beck and call makes sense to me as a thing they would do if the alternative is you exterminating them.
This is a point that is necessary to make slightly unrealistic. You can't apply the realistic 'stay alive at any cost', because otherwise it would be open to serious exploitation. Game balance demands a limit to which the AI will give in to your outlandish demands, no matter how much you are pummelling them.
It would also work to have diplomatic effects on third parties if you enforce an overly harsh set of conditions on a defeated enemy.
Definitely.