"Maybe the fact Microsoft are starting to embrace Linux as a "choice" in windows 10 is not about giving the user choice"
It's primarily for user convenience. For instance Developers can run legacy *nix text command line type tools without the bother of installing another OS on something.
"but a get out of jail free card with a future bios change that takes away choice."
Microsoft don't control manufacturer BIOS in general.
"UEFI which was a good start but not quite there "
Which had little to do with Microsoft.