All VM images should move up to Hypervisor Gen2 because Azure have released a new VM size Dsv6 that only supports Gen2.
It is likely that the Dsv5 that is currently in use in the tRE will be retired at some point in the future. There is no warning of this at the moment, so it is not a priority.
The OUH Windows image is the only one that is still on Hypervisor Gen1. This also causes errors with the H100 image size as it requires Gen2.