> The flip side is the assumption that nobody in their right mind would pay for a chip that could be fully wiped and/or updated by end users.

Eh, TPMs are fully erasable -- well, the seeds that matter anyways, but not the public keys that sign firmware updates. There's a big difference between "fully wiped" in the TPM sense and "updated by end users" if the latter means "with their own code", but the latter is still OK if in the process all key material is lost that could be used to impersonate the original device.

I.e., an SE that users can flash with their own software should be OK provided that there is no way to impersonate the original SE after doing so. I've no idea if that can be the case for SEs, but it definitely could be for TPM-like devices.