The cool thing about proxmox is that it is - again - "just debian" so there is really no vendor lock-in. Yes they do have commercial support/update subscriptions but the community offering is open (https://github.com/proxmox). So I do not worry too much about lock-in or monoculturalization. At the end of the day it is a wrapper around fundamental components of Linux. They do not have any proprietary secret sauce that would F you down the road.

Correction I see now that the projects you reference are Solaris based. I am down with that cause too - but if you are a BSD/Solaris shop expect to do a lot of things on your own. The linux virtualization space is substantially larger (not necessarily suggesting it is better...)

My impression, strengthened by https://wiki.smartos.org/managing-instances-with-vmamd/#usin... , is that SmartOS preferentially operates at the per-host scale, which is probably a disadvantage in a datacenter setting. (I don't know enough about MNX Triton to comment)