I don't see why a TPM couldn't be open? Nobody makes open-source TPMs (because they're put inside CPUs or attached to motherboards with specific pins and protocols) but in theory you could just do it. All you need to do is make sure any secrets stored get wiped permanently whenever you flash new firmware.
It'd be similar to secure boot: usable by default, but reconfigurable so that you can bring your own keys and signatures, putting you in complete control of your hardware, to the point where even the manufacturer no longer has a say in what's running and what isn't.
It'd be similar to secure boot: usable by default, but reconfigurable so that you can bring your own keys and signatures, putting you in complete control of your hardware, to the point where even the manufacturer no longer has a say in what's running and what isn't.