When they started FP, you could get them for ANY Disney admission media with strips, even ones that were expired. No THAT was a loophole to exploit.
The question isn't if they will let you get FP+ with old media. I'm sure once I get to WDW, they will hook me up just fine. The "if" is when can you do that. Can you call in 2 months ahead and give them the number off your ticket, and get that transferred to a Magic Band, so you can schedule FP+s. That is what I don't think you'll be able to do. There is no way to get a biometric reading to match over the phone. They can't control that, so they likely won't do it.
This will be a huge lowering of value of non-expired tickets.
Jason