Even if SHAKEN/STIR was added to SS7 and H.323 it's not clear it would be added to any of the software for the remaining TDM switching hardware. Those platforms

Even if SHAKEN/STIR was added to SS7 and H.323 it's not clear it would be added to any of the software for the remaining TDM switching hardware. Those platforms are in sustaining support and many of them are unlikely to see any software updates at all in the remaining ~15 years they have before being turned down.