In my current company we are just starting with Phabricator. People are still learning their way around, but I already have few engineers (smart, awesome, capable, etc.) coming up to me and asking if it's possible to have project field required(maybe soft with a rule in Herald). Having a rule that send notification / email doesn't really do much - engineers tend not to notice notifications when tasks bounces back to them or they notice that in a few days. And having someone on the team look at such tasks regularly seems inefficient when you have a small team.