That's how I read the proposed amendment to Michigan Rule of Evidence 611 that was apparently adopted today:

The court shall exercise reasonable control over the appearance of parties and witnesses so as to (1) ensure that the demeanor of such persons may be observed and assessed by the fact-finder, and (2) to ensure the accurate identification of such persons.

Note, though, that the Detroit News reports that "The Michigan Supreme Court today adopted a court rule that allows judges to prohibit witnesses from wearing veils in court." Perhaps the adopted rule was different from the proposed rule I quoted. But if it's the same as the proposed rule, then it sounds like judges must prohibit veils for testifying witnesses, since the rule says "[t]he court shall exercise reasonable control ... so as to ... ensure that the demeanor of such persons may be observed and assessed" (emphasis added).

I should note that there's a lot of controversy among experts about whether observing a person's demeanor really does help laymen assess the person's credibility. I have seen claims (I haven't researched this closely myself) that in fact observation is completely useless except to those who are trained in certain ways. But the importance of demeanor evidence has long been assumed by our legal system, whether rightly or wrongly, and this decision seems consistent with that assumption. It may even be necessary if that assumption is accepted, unless letting the witness testify veiled but discounting the testimony is somehow made to work as an option (and it's not clear to me that it can be).

Thanks to Rob McEachern for the pointer.