Sorry not to reply sooner.
"heavy NF and MH domes are the commonly used shelters for sleeping in places like Denali" Yes domes are favored in high winds and mountains because they have less steep walls. Also that's what's been on the market, although half cylinders (in the old days these were the Early Winter designs and Stephenson Warmlght tents) are also coming back.
"Do you have an opinion on why pyramids aren't used as commonly for sleeping."
Yes, I have plenty of opinions! Pyramids are old style and more fussy to set up. Domes are super easy, pitch, place and anchor. Also easy to clean -- just shake them out.
"Would you or have you used a pyramid in places like Denali?" Yes, if weight was the primary factor and I was planning on spending less than 30% of the days tent bound. However, a pair of friends/climbing partners took a BD Megamid to 12,000 feet on AK's 16,000 foot Mt Sanford in February. A bad storm came and eventually blew away their 'mid, leaving them "naked" so to speak. Lost both sleeping bags and all fire. Epic self-rescue ensued. But a good illustration of why floorless pyramids are not poular on big mountains with high winds.
"Do you think that sod clothe/snow flaps are useful/necessary or frustrating? " I have been in post production mods with them and have them on my old Dana Design Nuktuks. Not really a fan. They get dirty and don't seem to be worth the additional weight to me.
" Do you see a value in wall ties, and where do you think that they are best placed." Yes, but I am not knowledgeable to where they should be placed. If any of my floorless pyramids have them (I have BD Megamids, the Arcric 1000 cuben fiber mid, Nuktuks, and Golite Hex3, maybe some other custom jobs, too) and if those have them Ihave never used them.
"Do you use a bivy/bag cover when using a pyramid during mid winter conditions? " My favorite set up in winter is a synthetic hooded puffy jacket worn inside a summer down bag inside a synthetic non-zip overbag (I have ones with insulation all around and ones for 2-4 people that we all pile into; use depends on temp and people and what we're doing).
" Is convection or moisture a bigger problem in mid winter mid life? " Hmmm. in mid-life (i.e 35-55 years old) I think moisture is the problem :) Kidding aside -- by Convection do you mean convective heat loss? As in wind? In snow that's easy to solve by shoveling snow around edges. I find moisture is less a problem since the snow absorbs humidity.