A known limitation of the Proxmox power driver, is the inability to change the boot order of VM’s through MAAS.
As it is, if you want to re-commision or re-deploy a VM, you have to go into the settings page of the VM in Proxmox and change the boot order to ensure the VM PXE boots. Then once you’re done deploying, you have to go back into the settings once more and change the boot order again to make sure the VM boots from harddisk again.
Optimally, MAAS should be able to change the boot order as needed (PXE boot/Harddisk boot), thus eliminating the need to change the VM settings in Proxmox every time. MAAS can already do this with other power drivers, like Intel AMT and ESXi.