Currently, you can book ADR's without confirming you have tickets in any way... I'm wondering if they won't just keep the same policy in place. There are various reasons why people might not buy tickets till they arrive at the gate... I can't imagine they'd be stupid enough to alienate those people.
With a supposedly "dynamic" and "real-time" system like NextGen, it's possible that as FP windows approach for names that don't have active tickets tied to them (say, a couple hours before?) those FP's could go back into the pool to be grabbed by someone else attempting to get the exact same FP.
But BOY do a lot of things have to go right for that to work smoothly.