Although, I suspect if AR really becomes a thing, it will be in a form-factor with actually physical transparency. Nreal is the design to beat, not the gaming headsets.
If the display is already transparent, adding a layer of pseudo-transparency to the interface seems kinda pointless.
The thing is that passthrough and optical AR compete and might always compete as each one has advantages.
The optical AR system is always going to be transparent to the outside world so perhaps a vendor that expects to sell both kinds of device will add transparency to the passthrough device so it looks "the same" as the optical device.
In that case the UI should have all-over transparency, rather than some limited transparent elements, right? And none of the complicated optical effects.
Although, I suspect if AR really becomes a thing, it will be in a form-factor with actually physical transparency. Nreal is the design to beat, not the gaming headsets.
If the display is already transparent, adding a layer of pseudo-transparency to the interface seems kinda pointless.