So I was coding along, adding some functionality to an interface, and the thought struck me that an inspection would be handy to show abstract methods for which there are subclasses which contain no implementation of the method. Call it something like "Abstract method not implemented in all subclasses". This would be fairly easy to do technically, and I wouldn't even have to code a quickfix for it, as the existing "Implement method" intention works just fine. The main value would be quick highlighting of places where more work needs to be done, always a good thing. It's also fits nicely with the existing "Interface never implemented" and "Abstract class never implemented" inspections, giving you great insight into places where you've left incomplete work. OTOH, there are some arguments for not doing it.
1) The code has no actual issues at the point of warning, only in the incompletely implemented subclasses.
2) The incompletely implemented already flagged as compile errors. I've stayed scrupulously away from reporting things that would be compile errors.
3)JetBrains presumably could have made this a built-in inspection, rather than a built-in intention, but chose not to. What do they know that I don't?