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I read somewhere, probably on here, that the factory fitted support rings are not the same as the aftermarket ones.  Maybe put on hot and shrink as they cool down, I can't remember.  The support rings on the hub I bought three years ago are not a lose fit, Thorn were not building wheels at the time (Pandemic) so I followed their example and built them that way myself, the rings haven't fallen off yet!

Are you saying that if you buy a new hub, the support rings are already installed and fit tightly?

Dave W (former employee at SJS) has commented on this forum that rings were available to dealers but not to retail customers that required heat to install.

I built up my own Rohloff wheel, I would still lace it up the way Rohloff says to, if I built one tomorrow.  I was unaware that Thorn had changed their lacing pattern this way.  But I am not looking for a new bike, have not looked at new Thorn bikes since before the Nomad Mk III came out.

I recently got some Marathon Mondial

I haven't used those, or the Marathon XR they replaced.  They have a huge reputation for longevity, but I've always wondered at what cost.  Is it just weight?  Or have they sacrificed anything else in order to be so hard wearing?

Are you saying that now Thorn builds Rohloff wheels so that the heads are all facing outwards? 

Yes, at least on the larger wheels, like this

If so, the new flange rings that are provided with the hubs would fall off, you need some spokes on the outside of the flange to hold the flange rings in place.

I read somewhere, probably on here, that the factory fitted support rings are not the same as the aftermarket ones.  Maybe put on hot and shrink as they cool down, I can't remember.  The support rings on the hub I bought three years ago are not a lose fit, Thorn were not building wheels at the time (Pandemic) so I followed their example and built them that way myself, the rings haven't fallen off yet! 

I bought a C17, did not like it, the rubber was much stiffer than other C17 saddles that I had looked at, it was to hard.

Later, I bought another C17 all weather version.  Did not like it either, even though the rubber was softer than the first.  Just mentioning this because the All Weather version has a smoother surface than the first one I got that had the regular surface.  You might consider looking at the All Weather version to see if you might like it.  A non-leather saddle might hold up better for that much riding for your planned trip, it would be much more maintenance free than the leather saddle.

I agree with Dan, the saddle clamp and the saddle rails should mate nicely without causing undue stress.

I have never had a saddle rail break.  I would think that a Brooks on a suspension seatpost would be less likely to break because the suspension should reduce some of the stresses that the saddle has to deal with on a rough road.

I know you said you already ordered a saddle, but since you asked, I have not used a Cane Creek short travel seatpost, so I can't comment on how that compares to a sprung saddle.

But I have used a Flyer and several Conquests.  Almost all of my riding is on Conquests.  I think the Conquest and Flyer share the same springs.  I am about 80 to 85 kg.  When I put my weight on my Conquest and sit somewhat upright, I think that I deflect the springs by 5mm at most.  My point is that these saddles do not deflect that much and I suspect that the suspension seatpost will give you much more cushioning.

Where I think that the springs perform best is on paved roads with a rough surface.  In USA we have some roads with a surface called chip seal, those roads cause a lot of vibration and a sprung saddle is pretty nice on that.

I do not know what your planned tire width is, but the wider the tires, the more cushioning you get from the tires.

I am considering buying a suspension seatpost for my Lynskey touring bike, that has 37mm tires and I usually pump them up pretty hard when I am carrying a load. 

I have ridden my Nomad Mk II with heavy loads on 57mm wide tires and the only times that I thought a suspension seatpost would be nice on that bike was when I was on the type of roads that cars can't drive on because the road was so rough.

First photo attached, this was the only time that I thought a suspension seatpost would be nice on my 57mm tires, look at the road surface in the photo.  When you see something in the road that is smaller than a tennis ball so you do not bother trying to ride around it, that tells you that you are on a a rough road.

Second photo, you can see how rough that chip seal road is, the shoulder is much rougher than the road surface where traffic has smoothed it out more.  Here is where I think a sprung saddle works best to smooth out the vibration.

Mine has leaked from day one.  If I had known that Peter White was a USA warranty option back in 2013 when I bought my hub, I would have done this too.  Last time I tried to ship something to another country, the costs and paperwork convinced me to never again do that.

But mine has been out of warranty now for so long, I am sure I am out of luck.