Sure, but getting an IOMMU right on a complicated platform that didn't historically lean on IOMMUs is different than "the IOMMU is backdoored".

Why this isn't just a nit is, if you believe (say) VT-d is backdoored, a lack of IVT research projects isn't evidence of the absence of backdoors. Presumably, if the NSA is serious enough to backdoor Intel chipsets, they'll do it in a manner that a couple of independent security researchers can't black-box.