Technically the lack of dynamic current negotiation is already a problem, because plugging a 20A refrigerator into a 15A circuit will trip the breaker or even start a fire in older homes if the owner decides to put a 20A fuse on a 15A circuit. We just don't normally see it, because most appliances like microwaves are designed for 1200-1800W (10-15A) running on 15A circuits.