I've considered virtualizing my current hardware Opnsense router, mostly to save on electricity. But I fear the situation of needing to do maintenance or troubleshooting on the Proxmox host without internet. What fallback do you have?
I have a cluster of 3 Proxmox hosts, mostly to teach myself about clustering. I have two Vyos instances running VRRP between them. If the primary fails, the secondary sees the VRRP state change, runs a small script to bring up the PPPoE interface and we're away laughing. It syncs state, so people notice ~8-10 seconds of packet loss and everything just keeps going.
It's quite nerdy though. And all it does is move the single point of the failure to the switch (required for the hosts to talk to each other for VRRP etc)
Proxmox is so reliable in my experience though, but I don't tend to fiddle with it, just set and forget.
This is my main issue with pfSense/OpnSense. Even the dedicated hardware appliances are quite power hungry compared to some of the rather capable Linux ARM boxes out there.
For comparison, an 8 Gbps capable pfSense appliance (like the Netgate 4100) requires 40W-50W (max 60W), where the UniFi Dream Machine Pro, also capable of 8Gbps, has a maximum power consumption of 33W, which includes a 3.5" harddrive for UniFi Protect. Mine uses about 18W without the harddrive, and 22W with a WD Red.
A difference of 25W over a year at current european electricity prices (€0.5/kWh) means a saving of 219 kWh (€109/year). Considering that electricity has been as high as €1.12/kWh this spring, it could be even higher.
As for virtualization, while it's a great learning experience, it's probably more trouble than it's worth. I greatly prefer appliances for network.
Yeah, I'm in the same boat, but I doubt its gonna save much electricity, and whenever I patch ESXi (or Proxmox) the entire internet connection is down.