RGM idea: Class-type only

How fun/refreshing do you believe it would be if there was a mode where, for instance, only primary mages were available to pick? Or only primary tanks/assassins etc? The entire champion roster would probably need to be made available, or allow duplicate champs for the same team.

Another idea I have is a game mode where only, for instance, AP or AD items are available to purchase. A problem I see with this is potentially only burst champs being picked, so maybe it need some URF rules when it comes to CDR and attack speed