We are happy users of the azure-vm-agents-plugin, unfortunatley we often see that request for agent comes in bursts and that puts stress on the IOPS limmits on our jenkins master. We are bootstrapping data from our master to the newley provisioned slaves and the more slaves that are provisioned at a time the slower the provisioning. therefore it would be nice to have a limit of concurrent provisioning slaves.
This feature might also help with an issue I have seen where the plugin requested 20 VM's and that was too many cores for our azure subscription and thus no VM's were provisioned - with this we would get as many as possible...