I'm trying to remember so bear with me since it's been a few months....
Main one is that for GOG galaxy I have to use GOG galaxy via the vmware web remote console which is the equivalent of physical access to the machine. Any other access than that results in GOG Galaxy not working due to how their shitty launcher is programmed and they will never fix. No other launcher has this issue. I do use gogrepo to download all games as well but need the GOG Galaxy downloads too....and no I'm not going back to loading GOG galaxy on a physical machine. Worse comes to worse mabye a nested ESXi VM inside of a proxmox vm may work. bleh.
Interoperability between Proxmox VMs and client virtualization solution. Need to be able to export and import without issue and jumping through hoops. Need a virtualization solution on Linux and Windows with the same GUI on both that's not shit and that can import and use the VM straight from proxmox withut an BS. Solution needs to offer 3D acceleration on at least 2000+ guests for both Linux and Windows VMs without any bullshit.
Need to be able to copy and paste from guest to host and vice versa on virtualization solution on Linux and Windows. This is a nice to have since networking can solve this.
For Proxmox needs to supports DOS+ and for 9x+ needs to have additions and drivers and those additions and drivers need to be the same for both proxmox and the virtualization solution on Linux and Windows.
Need to be able to easily setup old Windows VMs without jumping through hoops on proxmox or virtualization solution on client. Select "Windows 2000", install. Done. No craziness tracking down which ver of KVM supports what or which OS supports UEFI,secure boot etc, changing x settings in x config. etc It should all be handled by the GUI.
Proxmon remote console needs to be as responsive as the ESXi remote console. VNC has been and apparently will always be shit compared to RDP assuming that's what it's using. I usually enable rdp on linux systems anyway but for proxmox itself I'll have to check again to see how responsive it is. I guess this could be qualified as a nice to have but I use remote console alot and would rather not have to put up with a lesser experience.
All the VM settings even advanced ones should be configurable via the GUI. I believe this may be the case like I said it's been a few months and I don't have proxmox installed. I do remember there being about a bajillion of them and identifying which one allows which OS to install and boot so thinking this one is a non-issue except for like most Linux use cases where you can't find any use cases similar to yours via web searching and nothing in the documentation.....
I didn't look into snapshots last I looked at proxmox. Snapshots needed for both proxmox and client virtualization solutions and those snapshots should be usable both on export and import by both. Not a dealbreaker but disappointing if not there.
The above is for using proxmox as a server and hosting my VMs.
As far as using proxmox for passthrou and gaming or game compatibility testing I didn't really have any issues with it and it was sufficient for that use case. Ideally interoperability between the VMS and a virtualization solution with the same GUI on both Linux and Windows and the same additions and drivers (and driver parity between both linux and windows guests) would be nice but not a deal breaker.
I'm not a fan of virtualbox, it's always seemed pretty shitty IMO but may be all we really have to abstract the burden of keeping track of managing all the settings to run a and manage a VM on a client machine now that Brodcom is going to further contribute to the death of Vmware.
