allow a user defined route (UDR) to catch smaller routes in one user defined route.
In a hub / spoke model in which many spokes are created with smaller ip spaces with multiple subnet(s) that need to forward traffic to the hub in exact the same way independent of the spoke, you would have to create specific return udr's to match the size of the subnet else the rule won't work in the hub. (and a 0.0.0.0/0 and a 10.0.0.0/8 wouldn't work / do)
It would be nice if you could set a flag on a UDR for instance to act as a catch al for multiple spokes. so if I had for instance a bunch of dedicated spokes within different subscriptions that had the following ip spaces appointed to them per vnet, 10.0.0.0/21, 10.0.8.0/21, 10.0.16.0/21, etc. and they forward internet to a nva at 10.0.55.4 and trusted traffic to an nva at 10.0.56.4. Trusted traffic would be forwarded to something in the hub which will have to answer back via the nva.
So Instead of making specific rules to answer them back via the nva scoped to the subnets they are coming from I would like to create a udr as 10.0.0.0/19 to return al traffic for the different spokes. This would reduce complexity and allow for better scaling in a simple flat networking environment.
Andreas sobczyk commented
+1 on this! In a Hub-and-spoke design where you want to route all traffic to a firewall you currently need to add a entry into the route table for the hub network subnets everytime you add a new peer network, making it much harder to ensure that all your spoke traffic is passing the firewall