hm - I'm at a startup with plan/release/build. The truth is...there are almost no abrupt new features. If something is truly a new feature - it's gonna move into planning. We've had 1 instance in my 8 months on the team with an abrupt-ish full-on feature (that I know of at least). I worked on it - there was a lot of communication with me about the scope/timeline/expectations. The feature fit into an offering we have at a beta stage - so it helped us expand something we were working on broadly anyways and was in service of winning a particularly good logo/customer. Again - this is super rare for us, but broadly - we simply communicate priority and have alignment about working on the most important things first. Generally, someone is picking up the feature that's coming off some piece of work or is working on something low stakes. Other abrupt stuff comes up - generally if it's limiting a customer's ability to utilize our product - we prioritize it.

I think you want to have a culture where abrupt new features are incredibly rare.