Why would it wipe billions from their share price? Both Linux and Windows were available on Mac hardware prior to Apple Silicon.

If I play devil's advocate, the only reason I could think of is that supporting Linux signals to investors that Apple is offering a key to bypass their API moat, perhaps sacrificing a longer term vision of vendor lock-in.

By contrast, I can imagine investors would get upset if the iPhone had an unlocked bootloader and allowed Android to be installed - but that's because the App Store is a significant revenue stream for Apple. I don't think there is a parallel on MacOS that investors could point to as being upsetting.

If anything, optional support for Linux would lift the market cap for Mac hardware as it would close the only pull that other laptop vendors previously enjoyed.

In reality though, just like is historically true, 99% of people would continue to use MacOS. Only SWEs, enthusiasts, gamers and some number of Windows refugees would pick Linux.

Though I am 100% behind legislating Linux support - EU are you listening?