I have a lot of doubts this will ever happen. If I'm not mistaken, the relative open-ness of modern PCs (being able to build a gaming pc for example) is basically an accident. It would be nice to have some regulation backing it up, too.
It all started with IBM publishing detailed technical information for the very first PCs, i.e. the PC, XT, and AT. This included full schematics for the motherboard as well as the BIOS source code listing (it was copyrighted, but only in the "copy" sense.) Companies like Intel were also far less secretive about their processors' documentation in those days. This started the whole "PC clone" industry, and things like the ISA bus became a de-facto standard as a result. There was far more cooperation between companies to enable expansion and compatibility, but I guess these days they are more interested in the amount of additional profit made by forcing consumers to buy an entire new system instead of upgrading parts, hence trends like soldered RAM and storage, and some companies (notably, one with a fruit logo...) outright attempting to squash the aftermarket/third-party ecosystem.
ARM (and many of its competitors, including MIPS and RISC-V) being only an IP core means they get put into lots of different SoC hardware where the only thing they have in common is the instruction set.
(There is "embedded x86", but as the reason for choosing that is compatibility with existing hardware and software, those do tend to be quite PC compatible, if only missing some of the normal peripherals.)
