True Left

"contemporary Islamic dress codes as visually sexually dimorphic in their own right on account of such codes employing different articles of clothing for men than for women"

The key is to clearly explain that different dress practices for men and for women does not necessarily correspond to celebration of sexual dimorphism, so long as the particular practices are designed to disguise (rather than accentuate) the sexual dimorphism of the practitioners.

"those dress codes reduce the visual sexual dimorphism of women without simultaneously reducing the visual sexual dimorphism of men to the same degree."

This is a valid criticism and one which I have raised myself in the past. Why should women do more work than men in dressing up? They should not. But the point here is that Western dress also requires women to do more work than men in dressing up, yet this extra work is done by women in order to increase their visible sexual dimorphism! Thus both Western and Islamic dress codes (sadly) require women to do more work, but for opposite objectives, and comparing only the objectives allows us to conclude that Islamic dress code is at least trying to aim in a good direction (albeit with much room for improvement).

"an idealized version of the Islamic dress code according to Mohammedan standards to the audience receiving our message. What might such a dress code look like relative to the existing ones?"

The main issue is how to cover hair. I personally would say that hats/turbans are adequate, though societies which want headscarves should be allowed to keep using them on the condition that men be required to wear them also. I also support the alternative of shaving the head.

Related:

https://trueleft.createaforum.com/colonial-era/re-genghis-khan/msg4142/#msg4142