Interesting thread for me not being from a cold area. Lots of ideas and so I enjoyed the different opinions.

I move from cages long ago. Clippless was a revelation. I had more problems with my toes going numb on long rides from pulling up not from temperature. Arches hurting from soft shoes.

Recently (over a year ago) I switched to flats on my mtb with 5 10 shoes. I was surprised at how positive the "lock in" the pins were with a flat specific shoe. Getting off the bike is much easier and I get why the OP was going in this direction. I was surprised how quickly I adapted to not trying to pull up. When I ride clippless now I think I pull up more than I did in the past just because I miss it a bit from being on flats. The wide platform flats keep the surface where your foot interacts with the bike less inclined for arch pain even on long rides.

If it were me I would go with the platforms some good warm hiking boots and ditch the traps

At this point I am 80 percent of even more on flats with my MTB. Still on clipless for my road bike.

If I were to tour and I have done a few over the years I would go with spd and carry some shoes. It is true they do not pack well. I would stuff socks and other items in to maximize space. I just would not want the same shoes 12 hours plus every day.