But that's how it already works.

If you install Windows first, Microsoft takes control (but it graciously allows Linux distros to use their key). If you install Linux first, you take control.

It's perfectly possible for you to maintain your own fully-secure trust chain, including a TPM setup which E.G. lets you keep a 4-digit pin while keeping your system secure against brute force attacks. You can't do that with the 1990s "encryption is all you need" style of system security.