Time now for only a short answer.
Easy for someone without a problem, and with nearly unlimited spare parts, to say a solution is not necessary!
It is a bit dramatic to suggest that allowing a little more camber will make a significant difference in failures of related parts. We are talking tiny differences, relevant when it comes to car balance and getting that last tenth or two in lap time but not with respect to stress on parts.
The fact that you are convinced everyone will end up running more than they do today tells me that unless I can get as much as the best “legal” car I am at a disadvantage. Read that a few more times and then explain why I should accept that when the remedy is so simple.
Why should a racer go to the considerable time and expense to replace a subframe that has them limited to 2.9 degrees?? Seriously, imagine that your race car is taking up half of your 2-car garage at home and your tools, tires and spares the other half so the wife has to park outside. You have a real job and a life other than racing. Some knucklehead clipped you at the last race, costing you a wheel, control arm, whatever, and maybe slightly tweaked the subframe. You won’t know for sure until you replace the other parts and try to set toe & camber, even assuming you have the tools to do that at home. Sure enough, you can’t get as much negative as before. So now you need to find a replacement and hope it’s OK as you give up how many evenings to pull the diff, brake lines, all rear suspension, etc. so you can drop the subframe. Oh, and that hasn’t been off since the car was new so have fun with those nuts. Then you notice that there is enough slop in the mounts to allow some degree of alignment relative to the chassis centerline and front frame, or more likely misalignment since you have no way to measure it.
Not everyone has OPM, East Street, Advanced or one of the others taking care of their cars. Most of the front runners do, but this isn’t a club only for them or the well-heeled who can just drop the car off somewhere to have it fixed.
Seriously spend at least 10 minutes visualizing that guy going through each and every step himself to identify and replace a rear subframe, by himself, at home. The time, the expense, the missed race weekend, the pissed wife. Put yourself in his shoes and imagine doing that while thinking how a simple rule change could have saved him from all of it, but the people in power said “NO!” without so much as a substantive rationale.
You really don’t want the long version.