Our issue: The amount of time for provisioning a new instance takes a long time because of steps like certificate, encryption, domain join, TLS and Cipher changes,...
Solution: In our use case, we end up to have two different VMSS for the purpose of deployment, re-imaging or blue green use case. Please note in our region (Azure Gov), we don't have access to low priority VMSS or Azure VM Spot to do pre-provisioning.
It only makes sense to have two different scales set behind a cloud-native load balancer (or private Traffic Manager - which is not available yet) to route request base on the VMSS prob readiness.
Ask: How can we have two Azure Virtual Machine Scale Set behind a load balancer
I never tried this, but I dont see why this would not work with Standard Load Balancer (not basic, basic one is limited to 1 vmss, afair), if it doesnt - it should work with Application Gateway.