I would be willing to try it if there was a good comparison what Proxmox can do (better than vmWare). I have no pain point that is driving me to look for alternatives and I have not found a compelling reason yet. Nor a good comparison at all. Even the one on the Proxmox side basically just says 'But it's linux' and thats their main selling point - at least thats my understanding.
Happy to be corrected and or enlightend
For an all-in-one, VmWare doesn't do containers. So you have to pass an HBA into a VM for storage, then export that storage using network protocols to the other VMs. That adds network stack overhead and VM overhead.
Proxmox manages the storage itself, so there's no overhead there. It also means that you can use onboard SATA ports as you don't need to pass controllers around via PCI-passthrough. Then if you use containers, you can bind mount storage locations to them. No network stack required, just a simple kernel call, so performance is not as impacted.
I have read reports from people that got some decent performance gains that way. Now, if you don't use containers, say you need non-linux, you are in a similar situation to ESXI. But one layer of VM is removed. I don't know that it's a big difference in that case. VMs are pretty efficient these days.
IMO, it's not so much better as it is a different set of tradeoffs. It's also open source, which matters more/less depending who you ask. I don't think I would advise people with a working ESXI to switch everything over. But I do think it's worth a look on a test box or VM to experiment with.