David, you say you are not talking about CAGES, and be that what it may, anything involing the cage structure falls under the cage unbrella, and that is the responsibility of the CRB.
Big picture thinking says that there should be a strategy that sets a "path" for a car to go thru as it moves from one category to another.
Counter to that is the fact that street cars, (the starting point) weigh more, and often travel faster than many full tilt "race cars" do.
So, on one hand it seems that a cage could be added on to over it's lifetime as it went from category to category, but the needs of the different categories aren't linear, unfortunately.
Of course, the rules have been modded over the years as needs changed, and there are some issues that exist.
It is my understanding that the CRB is aware of the issues, and a big picture review is in the not too distant future.
My suggestion is that, within the SCCA, the CRB holds responsibility for the cage and side protection rules, and you should expect them to respond to your queries.