drop Ready condition and allow old gateways to be present if mutability fails

Author: dprotaso

geps/gep-1651.md

@@ -70,11 +70,13 @@ signal the default routability using the Gateway's `status.addresses`. See 'Stat
 for more details.
 
 ### Mutability
+
 Implementations MAY prevent end-users from updating the `routability` value of a Gateway. If
 updates are allowed the semantics and behaviour will depend on the underlying implementation.
 
 If a Gateway is mutated but does not support the desired routability it MUST set the conditions
-`Accepted`, `Ready`, `Programmed` to `False` with `Reason` set to `UnsupportedRoutability`.
+`Accepted`, `Programmed` to `False` with `Reason` set to `UnsupportedRoutability`. Implementations
+MAY choose to leave the old Gateway running with the previous generation's configuration.
 
 ### Go
 
@@ -136,7 +138,7 @@ type GatewayInfrastructure struct {
   // Implementations MAY prevent end-users from updating the routability value of a Gateway.
   // If updates are allowed the semantics and behaviour will depend on the underlying implementation.
   // If a Gateway is mutated but does not support the desired routability it MUST set the conditions
-  // `Accepted`, `Ready`, `Programmed` to `False` with `Reason` set to `UnsupportedRoutability`.
+  // `Accepted`, `Programmed` to `False` with `Reason` set to `UnsupportedRoutability`.
   //
   // It is RECOMMENDED that in-cluster gateways SHOULD NOT support 'Private' routability.
   // Kubernetes doesn't have a concept of 'Private' routability for Services. In the future this may