I'd guess this feature is already planned, as other inno"games" have it (i am playing FoE). What would be your suggested "reward" for attacking a neighbor?
PvP is discussed in this thread (click). Because many players stated in that thread that they wouldn't want their cities to be plundered, the idea of a PvP Arena that's separate from your city has been forwarded. However, you can still discuss the plundering part of PvP in the referred thread. I'll close this thread as a duplicate.