I think you got more than enough advice here, and as you see it can be boiled down to two opposites: 1) bring way less than you're planning to; 2) you'll be fine with that.
I say do whatever you feel is right. Whichever you choose, it will probably turn out to be the wrong choice, but you'll have learned the best way and found your best bet for the next trip.
Just remember to share some photos (and to bring some ORS and broad-spectrum antibiotic)
That has always been my approach to this. I started this thread hoping to hear the thoughts of others, and the response has been great. Many thanks to everyone who has contributed!
In deciding on what to bring in terms of kit, I never have felt like "Please help, I don't know what to bring." The thoughts of others have been very useful in helping me think about how to fine tune my kit but my thoughts on what to take were more or less definite from the get-go.
I feel like what I'm planning on taking is near the upper limit of what is reasonable and manageable -
for me. For others, my "war load" of gear may be utterly insane.
I probably have a higher tolerance for carrying gear, thanks to the backpacking and other outdoor adventures I have been participated in. The amount of kit I will take to Mongolia doesn't hold a candle to the amount of gear camping gear that I pulled on a sled during a week-long winter photo/camping trip in Minnesota's Boundary Waters in my younger days.
Leaving the XPAN kit at home would lighten my load significantly - but if I don't actually use my XPAN on this photographc opportunity of a lifetime, what's the point of having it? That point is hard to argue against in my mind.
At any rate, thank you again to one and all who have contributed to this discussion - it has been quite illuminating.
... Whichever you choose, it will probably turn out to be the wrong choice...
@Andrea - more true words have never been spoken!
😀 When it comes to any photographic endeavor involving travel, Murphy's Law will always be relentlessly and maddeningly in full effect. Sometimes it seems that screwing with photographers is Mr. Murphy's reason for living...