Often I invoke the completion list to view all available methods (on an object) and am looking for a particular return type. It would be great if I could somehow filter down the list by return type. Currently I can only begin typing (more letters) and filter by method name.
I don't exactly how it should be invoked, but I consider this a highly useful feature. It's similar to the smart completion where you only get suggestions that match the expected type of the current expression. But with my suggestion you have more controll and it works even if there is no expected type.
I don't know how it can be implemented, my vision is something like Alt+Enter intention action on method lookup to filter lookups by this lookup return type, however I'm not sure is it possible in current completion API. You can create a ticket, maybe somebody finally will do it, but I can't promise more.
You can do it for both Java and Scala. If somebody does it for Java (or possibly gives better resolution, why it's impossible to do), then I'll do the same for Scala.