While I maintain the focus should be on how to get more drivers into on-road, this thread seems to keep diverting back to how to re-slice the existing pie instead of growing it first.
That being the case, I am in agreement with 21.5 TC. IF 21.5TC became a thing, then drop 17.5 and make it 13.5. I know that lap times are similar, but that's kinda the point. 13.5 is so close to 17.5 speed wise, but you aren't maxing that 13.5 out on most indoor carpet tracks. And by having a motor that has just a smidge more power than really needed, the motor war issue will be almost non-existent (at least for a while). Make 13.5 "super stock" or whatever you want to call it, and then make the 21.5 "stock" class (little to no sponsorship allowed, if you dominate the class for an extended period of time, you are asked (not forced) to move up.
The issue comes in that we already have a pretty fun 21.5 class. So maybe it's just time to drop 17.5 TC and make it 13.5. That now leave us with 4 TC classes, most tracks will probably only run 2 or 3 of.
I am just getting into 17.5, and I think it's pretty fun. But there are a lot of drivers that are pretty much maxed out in 17.5 and if they had somewhere else to go besides mod probably would. But then again maybe all these drivers like knowing that they are the best of the group and are scared that if they stepped out, they would no longer be on the podium.