As I understand, switching a gateway from V2 to V3 only means changing the server hostname (apart from registering on the V3 system, of course). This will need to administrate the gateway’s setup interface.
Reconfiguring gateways already deployed at locations that are different to reach will in many cases become a serious problem when the time has come, I’m afraid.
I wonder if it would be possible to automatically switch V2 gateways to V3 (of course still using the old packet forwarder) by simply DNS-resolving the old hostname router.eu.thethings.network to the new eu1.cloud.thethings.network (and similar for other regions)? If the V2 world is shut down anyway, the host entry is no longer used, isn’t it?