Looks like the dual-sided factory install for GRX is now available from 4iiii for $649 CAD. 4iiii Shop - Canada: Dual-Side PRECISION PRO Powermeter - Factory Install - Shimano - GRX FC-RX810.
I’m currently running the Rotor 2inpower DM powermeter on my gravel bike with the 46/30 chainring and an 11-36 cassette with SRAM eTap HRD. Gearing has been pretty good except for a few bikepacking trips, and have been looking at moving to GRX on my next bike, but the whole powermeter issue has been a big question. This thread has been really helpful! Thanks.