I am not entirely sure if i understand your question, do you mean to show how many cpu on the host pve server, and the remaining cpu to assign? Similar to how you see storage now?
The thing is, with the Virtualization you can overcommit CPU, and many many productions depends on this,since it's not expected that all vm will consume the assigned CPU all times.
IMHO, I think the correct way is to monitor your vm usage, use tool like lscpu and manage the VM CPU assignment depends on their needs.
I hope I understand your question correctly.