I'm not so sure the Enterprise featurettes were shot in 4:3.
They were presented to us on DVD in that format but they were in fact shown in letterbox 4:3.
For whatever strange reason they decided to do that I don't know.
The interview segments were almost definitely shot in 16:9, HD most probably.
I've only seem some of Enterprise on DVD. The Digital Bits review didn't mention if it was letterboxed or not.
6 behind-the-scenes featurettes (all 4x3, DD 2.0),
Star Trek: Enterprise
The Complete Fourth Season
Perhaps someone can let us know who owns all 4 seasons if it is letterboxed featurettes ? Or point to a review that states full frame or letterboxed for the featurettes for sure.