In addition to concerns others brought up like differing affixes, etc., this doesn't really even make sense. Most keys (particularly among the "majority" you mention below the 20+ range) aren't bricked due to the timer. They're caused by poor play, lack of communication, butt pulls, DCs, etc. Adding to the timer is mostly going to "balance" things for groups that are mechanically solid but can't push enough damage or get set back by wiping on a particular trash pack/boss- which is more of a high end concern overall.