"But why does that have to reflect itself back into something like the C programming language, which is intended for general-purpose programming?"
It is highly likely, especially in the world of IoT, that an FPGA or microcontroller could define structures and/or data with custom bit sized integers that were defined that way to function with limited RAM or limited NVRAM or EEPROM on the target device.
So the IoT device needs to have its data interpreted or 'firmly packed' before being sent to the device. It's much better if you can define the data structures and other things using the same C code for the FPGA or microcontroller *AND* the thing controlling it. Yeah, been there, done that. See my earlier post.
And, yeah, IoT makes this even more important to consider.
If LLVM implements it, gcc will no doubt follow. I use llvm with FreeBSD already, so good news for me if it gets in there this time. If it can be made a standard for the C language, that'd be awesome! [but yeah I'd expect some changes before that happens - committees need to "do things" after all]