For the FAA, AC 23.131-1C para 17.4 and AC25-11b (more tangentially in a couple of places) both discuss "decluttering" displays when in unusual attitudes (I think there's another AC which parallels AC23.1311 for part 25, but I can't find it right now). Suffice it to say, for those calling upon the "engineers and designers" to address this, there's already a bunch of guidance out there which does influence current designs. Indeed, one item for debate is what needs to be decluttered and what needs to be kept; something that is distracting clutter in one case might be the vital piece that completes the mental picture for the crew in another....