Sorry that no one has responded to your post yet. Hopefully I can clarify the understanding of your internal provisioning certificate, however.
The lifetime of the Root CA hash you embedded in your Intel vPro clients' firmware is more or less correlated to the lifetime of your Enterprise Root CA's certificate. Since the hash that is validated, is the one from your root CA, and not the provisioning certificate itself, each time you rotate out your provisioning certificate (eg. every 1 year), the root CA's certificate hash will remain constant.
In short, look at the expiration date of your root CA certificate to determine the last date you can issue provisioning certificates under that root cert. If your root CA cert doesn't expire for another 20 years, then you can safely re-issue new provisioning certificates from your subordinate CA until that time, that chain up to the root CA.
I hope his helps, and also hope that I haven't confused things even more.