> But if LLVM is available, they will get dollar signs in their eyes, and have visions of selling expensive proprietary compilers to a captive market (i.e. owners of their hardware).

This is literally not what is happening in the real world though. Counter example: NEC SX Aurora (literally developed in the open https://github.com/sx-aurora-dev/llvm-project), Fujitsu A64FX (free LLVM based compiler, $$$$ proprietary home grown compiler), AMD with hipSYCL. The reason for this if there was no LLVM available, the compiler would be totally proprietary. This from scratch compiler would have been more expensive to make leading it to not being available for free but instead licensed at huge cost. There has been no uptake of GCC for this role since it's inception. We both know why.

And even if a $$$$ using LLVM is made i would prefer that over a fully custom compiler. I can link against it like a LLVM compiler and you can learn a lot about a unknown platform from how LLVM compiles for it, making reverse engineering a lot easier compared to a proprietary compiler.