Apple has never locked down the bootloader on a Mac-series product before.

(But they have never not locked down a product with an A-series CPU - hence my concern)

They do allow you to run third party operating systems on Macs. For now.

Yes? This is a demonstrable fact?

Lay off the hater-ade for a second.

Uhh... you know when the Mac's were Intel they specifically made a tool for installing Windows on your Mac and shipped drivers for Windows.