Id be interested in trying one out. See how well the bladder cleans up with some oxy and star san...
They're just gigantic PET beer bottles, like a 500 ml plastic bottle x 20, they'd clean up fine.
It's how they're attached to the dispensing head that might be the issue, I haven't seen one close up enough to try and figure out how they connect, but I'm pretty certain the manufacturer has made them single use some how. Either that or you'd just need a Marks Keg Washer to Sanitize the PET bottle, and away you'd go.
When I first started looking in to these, I tried to find a manufacturer who was making just a PET bottle of this size, available by itself. Then one could fashion a corny cap for it and replace the market for used kegs with the newly modified invention, alas, no luck.
JQ