Yes. That thought did cross my mind. However, the RF baseband is an independent opaque blackbox already. As far as I know, it even includes an entire hidden operating system. But opening up the rest of the system, leaving the BB as it is, will go a long way to an open user-controlled system. We could adopt that as a stop gap measure until a longer term solution is found.
In the longer term however, we will need such a restriction on RF BB lifted too. Openness isn't just about modifiability. It's essential for security too. I'm someone who believes that security and granular restrictions can be implemented without being hostile towards users. This is why I don't buy Apple's argument that hardware lockdown measures like soldering on batteries, permanently gluing up ICs, etc are essential for miniaturization and security.
One solution for the problem you mentioned (devs over-boosting the RF output) is to have a one-time programmable power limiter after one of the final fixed-gain RF power amplifiers. (An example of a one-time programmable device is an anti-fuse FPGA). Such a baseband can be programmed to conform to the market country's regulations (or something even stricter) before assembly. This way, the developer can boost the signal as much as they want, but the device simply won't respond beyond the permissible limit.
Of course, all these are daydreams, because it has to be implemented by the baseband manufacturer. Unfortunately, their incentives don't align with our interests.