Among the many changes, the new rules would require batteries in consumer devices like smartphones to be easily removable and replaceable. That's far from the case today...
Its not really as easy for non apple repair techs to change the battery. If anyone but a certified person does I bet that would void any water resistance part of the warranty, possibly if anyone but apple specifically does it?
Easily changeable batteries that don't compromise water resistance would be really great, but that will definitely make them bigger.