16 wheels.....that's 4 sets. no wonder some are reluctant to a change.
I think the answer might be in this question: All of the Miata drivers that now run ITA; if you were reclassified to ITB, not IF but WHEN, what would you want the rules to be?

You are now running with 7". you have all your data based on 7" and now you have to unload your useless 7" rims (because ITA has probably allowed 17 X 8 in ITA) and buy 16 rims in 6" and then recalc all your data. It will happen as newer cars enter ITA and cars become reclassed.

Think about that and try to figure what is best for the class or better yet what is best for IT.

Dual classisfication might be ok if ther were weight allowances, but then that might null the reasons for reclassification.

The better answer is to allow any width based on fender clearance regardless of class and move on.

I do understand some concerns about the $ impact to some racers, given current inventory,etc. But the best answer for every car regardless of class is a rim width based on fender clearance. No restriction on diameter. a rule such as that wold be undisputable and continue to serve all It racers based on the car they built today, 30 years ago, and five years from now. (my opinion only)