TrustZone alone is much closer to a SecureBoot or TPMish feature than ME. It's possible it would allow implementation of an ME-like software stack running inside the TEE.

It's worth mentioning that there is at least one OSS implementation of a TEE software stack, OP-TEE, making this even less of an issue. Assuming your device/soc mfg doesn't lock you out.

http://www.linaro.org/blog/core-dump/op-tee-open-source-secu...

TrustZone is, for practical purposes, a little more open if you're the one designing the board. Most of the time, the crypto is opt in, and you as the final assembler control the keys.