Do I understand correctly that you're saying that the O-ring would be necessary even if the SRBs were constructed as a single long tube, instead of segments that are assembled together?
If so, would you mind expanding on that? I was under the impression that the only reason the whole O-ring and caulking of the joints was necessary was the existence of the joints.
[1] https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/...
Do you have a reference for this? Seems very intriguing to me. To me it seems the last thing you would want, under any circumstances would be to have hot gases coming out anywhere near the hydrogen tank and you'd make every effort to contain any overpressure until it exited beyond the hydrogen tank.
The following is a link to his book, but I actually heard a presentation from him.
https://www.amazon.com/Truth-Lies-Rings-Challenger-Disaster/...
The bigger issue here was the politics between Nasa and it's contractors. The contractors told them that the launch would be dangerous at the temperature, but they were ignored.