This may have already been suggested - I had an idea for an alternate, simpler approach to a backup proxy. Instead of bolting onto Windows (which is brilliant, I might add), what about a virtual appliance? Something really cut down, a thin linux appliance or something.
The reason for this is - we backup around 80 VMs each night, and to do so we have two dedicated, beefed up Windows servers acting as proxies. This obviously comes with the extra cost of Windows licensing, and the fat overheads of Windows. Also, we receive offsite backups from some of our clients, who may only have a single VM running on a host. Of course, the VM can't act as a proxy to backup itself, and the client doesn't want to pay for an additional windows license. This would fit perfectly in this scenario!
Veeam could even include the ability to automatically spin up preconfigured proxy appliances as required, leaving them shut down during peak hours and conserving precious RAM and CPU resources.
Just a thought