Hi Andrey,
I suppose it currently is for IntelliJ’s java plugin, but:
- How would libaries add new rules to the IDE? Or is the IDE limited to understanding the standard library with a fixed set of rules?
- How would rules be shared between IntelliJ and the Eclipse plugin in progress?
Anyway, I respect your judgement for not wanting to add bloat to the compiler. 
I guess such things call be handled by a static analysis tool like http://findbugs.sourceforge.net/ in a post compilation step for people that want it.
Cheers,
Andrew