Since the capacity of the rides don't change, if they continue to allow you to show up late so you can get that extra E-ticket ride, who is losing out on a ride? The guest that follows the rules that's who.
I for one would be happy if all the people that complain about enforcement of the rules don't go to the park any more. It will make the park that much more enjoyable for the rest of us.
The hourly capacity doesn't change, no. But to the best of my knowledge, Disney doesn't cut lines off well in advance of closing, which means that anyone who wants to get in line for the ride and "follow the rules" as they are presently writen will get on the ride should they be willing to wait and it doesn't break down. No one misses a ride. This theorized new way, someone does.
edit: Before someone catches it - yes, the person who previously might have been able to use an old fastpass to board 5 minutes to closing can still wait in the standby line of tomorrow, of course. What percentage of those people would wait standby? I have a feeling Disney has a better idea of the answer than me. All I know is that from my perspective, I'd probably lose out given my habits at Disney. But like Robb said, this is minutae about a system that isn't in place yet. We'll all know eventually.