Right now projects are very micromanagement intensive. You have to cancel any queued buildings (including upgrades) in order to start a project, then go back to a planet and re-queue everything when you want to start building things again. If you start a project at any time other than when an improvement finishes, you lose production. This management hassle is particularly time-consuming for the Yor, who need a project to expand their population.
Hence, my suggestion: have a planet simultaneously running a project and building things, and let the user choose what percentage of their production goes to construction vs. the project with a slider above the building selection window. Yes, this allows things like the Yor building things and growing their population at the same time, but really, the main difference between running Assembly for 5 turns and building things for 15 vs. running Assembly with 25% of your social production for 20 turns is that the latter involves less micro.