After chatting with Poly support and getting redirected to "Poly-Obihai" support (408-890-6000) and waiting on hold for 34 minutes (but who's counting) I got the following response:
The OBi1xxx and OBi2xxx series of IP phones are in the "End Of Life" phase and are no longer being manufactured. However, there has not yet been an official statement from Poly on this.
However, he assured me they would continue to be supported beyond the End Of Service cutoff date for the OBi2xx series of ATAs of 12-18-23. For how long past that date he didn't know. Have to wait for official statement from Poly.
Take that for whatever it's worth. However, he did seem knowledgeable and put me on hold for a few minutes to confirm things with engineering.