To add just a little to what spnkzss said, the car should be classed to a point to where it is not a rolling road block. It needs to be at least a mid pack car. In his exapmle I think an ITC car should be in HP.

It still could be a slippery slope as should an IT cross over to prod be allowed to remove lenses that have to be removed for prod but are ok for IT, pass door glass....there are a couple of others I can't think of off hand.

Most of the cross classing I have read about have been an "up" class jump. IT to Prod, Prod to GT.
SM to IT, me I just don't see why.