I just don't see what the big deal is about these?! They obviously have to be smaller than strollers, WAY smaller than the park issued double strollers. I can see the draw, especially for those of us with kids who are too big for strollers but who still need stuff to entertain them, changes of clothes, jackets, ponchos, water bottles, suntan lotion, etc. To whoever the above poster was who said "they" didn't need them and had always gotten by with a stroller and backpack - well, that's the point, if you have a stroller, you have somewhere to put everything, including your backpack if you don't want to haul it on all rides. I can easily fit an entire lunch including drinks, a complete set of swimwear for a family of 5, jackets plus ponchos under my stroller and it's a lightweight $30 one.
I understand the point about they're behind you, not in front of you, but how many times have you been plowed into by a stroller that didn't stop in time or wasn't looking where they were going? At least these won't be running INTO you. And I don't think they're that far behind people that it's as annoying as kids on the leashes who are dawdling 5 feet behind their parent effectively blocking off that whole area. I've never seen one that extended more than about 1-2 feet.
I just don't get the controversy. That said, no, I don't have any intention of bringing one to the parks next week even though all my boys have nice ones for school. They're just too bulky for me to carry when necessary, to maneuver and to fit on rides for me to ever consider one. And I don't think I'd be comfortable leaving them out like a stroller. But I really think they'd just inconvenience me, not others.
As to Disney setting a policy, they have, no rolling backpacks (at least you're theoretically not allowed to "roll" them). As to Disney enforcing a policy, well, that's where the problem seems to lie! I'll let you all know how bad they are next week!