Thank you for this feedback. The hybrid story is very important to us, and we are working to bring new capabilities for you to utilize. Stay tuned.
An error occurred while saving the commentNed Bellavance commented
This would be a very nice feature to add an existing VM to an empty availability set. The problem that I see is adding a VM to an existing availability set with other VMs may violate the availability set constraints. Imagine a situation where you have two VMs in an Av-Set and you would like to add a third. If the third VM already exists, it may be running in the same update or failure domain as one of the other two VMs. In order to add the third VM without violating the constraints, it would need to be moved to a different update domain or failure domain. Doing so requires the VM to be powered down, since Azure doesn't do live migration of VMs off their current host.
I have come across several situations where someone started with a single VM and later decided they wanted to add a second VM for redundancy, but they had not configured an Av-Set with the first VM. It would be nice to be able to create an empty Av-Set and add the first VM, then create the second VM in the same Av-Set. That avoids the constraint violation issues I mentioned above and makes like easier for the admin.