(I suspect the suggestion is mostly in jest, but if not...)|
Gonna go with a big no on this.
If you want to PK, do it in designated PK areas. You should not have the ability to interrupt others' daily activities by killing them. If the designated PK areas aren't active enough for you then that should be indicative itself of what the kingdoms would turn into. The cities needn't become deserted because PKers can't find enough victims.