Im in the same boat with cages as I am for trailers for street / strip cars.
If it has a cage, it better wheelie, and be at least in the 9's, same with trailered cars imo.
I know there's some "ill" handling cars that are probably in the 13's, and maybe 14's, but I'm thinking these late model cars with the right amount of power, and traction can probably make dozens of low 10 second passes, and look uneventful doing it. I guess it's the cars that shouldn't be at the track to begin with that insist on racing that ruins it for good cars.
Long story short is, I know Brian's car, and others similar to his run very good, and I cannot imagine it being considered unsafe enough to mandate a cage if he went a few tenths quicker than he's currently going now. I don't know when the 11.5 rule was set in place, but I'm betting the speed limit on the interstates was 55, and not 75, or 80 like it is currently.
I know completely stock vehicles can run quicker than 11.5 without a cage, but would you rather be next to a new ZR1 Vette, or Viper on plastic, big wheel compound factory tires, or drag radials. I'd put money that he/she would be more apt to stay in their own lane with drag radials. As a matter of fact, being next to a car like that at the drag strip, I'd appreciate it if they had a little suspension work as well to help them stay glued to the track.