I will think on this a bit more to formulate a more detailed response, but in the meantime
In fact, due to the nature of the approvals protocol the nodes are already executing multiple PVFs in parallel, and the amount that they are required to is a function of the number of availability cores in the system. We would like to see scaling via stuff like Elastic Scaling (fka Parachain Scaling by Parablock splitting) that allows approvals to validate sequential blocks in parallel.