Is there a mod that adds contracts to the game? I couldn't find any in the mod portal.
If not, perhaps a modder could make one? I think this is viable because it adds an interesting new feature and goals. Plus the mod doesn't have to stick to conventional gameplay design seen in other games.
For example lock a research branch behind a certain contractor and if you do "enough" with them, they'll allow you to research their branch.
"Enough" may be having good relations as in completing contracts or having difficult enough contracts that take items per second.
To satisfy those contracts you may have to build contract delivery silos or an earlier-game solution with buildings that just eat the resources for the contracts.