I don't think the companies who make on-road kits really want it to get big again. That's why a race quality sedan kit that could run in a local A-main or a national D-main costs $500 and a 2wd buggy of the same caliber is under $250 with an aluminium chassis.
I love 1/12 scale, but it will die soon without new blood that want to buy a $250 tire truer and spend $50 a month on tires, yet F1 rubber tires on WGTR have ruined the driving character of the cars. Pushing some random rubber tire from an 1/18 scale car into the 1/12th racing would kill the class dead in a week. A completely new rim and tire would have to be designed, tested, re-designed and re-tested then pushed on a rubber hating majority. I don't know the answer, but these are the challenges.
I have often wondered about a large version of the silicone tires I used to run on AFX/Tyco slot cars that would slide onto the stock BSR or CRC rims.
I'm sure the cost of carpet being double affects the track owners as well.