I've been trying not to post in this thread. You're not going to like what I have to say. That doesn't make me wrong though. You reference rally use as your experience with your Wing and why you're considering a different bike. At 6' 1" you're not really all that tall, but you're not saying inseam length either, so we don't know if you are short leg, tall torso or long leg, short torso or about the middle of the road. That makes a difference because most riders that say they don't "fit" on a bike are complaining about leg room, knees against fairings, etc.
I am wondering how much better life would be if I could find a decent rally capable bike that weighs enough less to justify the pain of switching to a new bike…
My current bike: 2006 GL1800. Highly reliable and highly ‘farkle-able’. Pretty well dialed in.
Pretty well dialed in doesn't really tell us what you've done, only that you feel it's that way. A GL1800 of that vintage needs some standard upgrades to really transform it's handling. Others have mentioned the
Traxxion products, which are excellent.
What have you done to your Wing?
You gave us a list to consider:
Replacement considerations:
Reliability - (nothing made in Europe need be suggested) Argue what you want, it's a small place with small distances and dealer network in the US is tiny compared to Japanese brands. Or HD for that matter.
Weight - (you're riding the bike, not pushing it around.) When during the MD2020 did you really feel the Wing was heavy?
Rider wind protection - (Nothing beats a pre- 2018 GL1800.) No other bike will have that pocket of quiet, still air like a GL1800.
Long distance comfort - (Are you new here?) Every bike requires some ergonomic adjustment, but any bike can be comfortable if you do the work.
Farkle-ability - (You meant to say "Availability of bolt on aftermarket parts") Because farkles used to be crap we made ourselves, and often that still applies.
Cost - (that's relative.) Tell us what your comfort zone is and it will eliminate the suggestions to buy a new BMW or HD. If those were in the running, you wouldn't be concerned about cost.
Stop asking questions and go ride some bikes. You have a lot of inaccurate ideas about the FJR, for example.
For reference, I rode an '04 FJR for a dozen or so 24-36 hour rallies, several cert rides and the MERA 10-n-10, (10 days, 12k+ miles), putting on 160k miles over 9 years. Not huge miles compared to lots of riders here, but enough to know that platform very well.
I rode several 24 or longer rallies, some cert rides and the '13 IBR on a '12 Super Tenere too, and know that platform very well. (110k miles over ~5 years. Also a little shy of 50k miles on a '15 Super Ten.
My wife put ~120k on a couple of GL1800s, I think the last one was an '08 or '09. Set up well, Traxxion suspension, windscreen upgrade, and likely other bits. I have a few thousand miles on that bike too, so have an idea of what a well sorted GL1800 can be.
My Beautiful Wife also put ~110k on a BMW F650GS twin, so I'm familiar with that and can and will call BS on any statements about how modern chains are just as good as a shaft. People that aren't riding rallies say crap like that. Lube your chain twice a day or set up a chain oiler, don't use a high Hp bike and understand that you will adjust the chain once shortly after new, then the next time you need to adjust it, you're nearing End Of Life and the clock is ticking. Lube is for the chain to sprocket interface, not the chain itself. And sprockets get replaced with the chain in sets. Quite frankly, the Math doesn't work on comparing Shaft to Chain. Shaft always wins if you actually ride the bike big miles.
I'm 5'11" and ~260ish w/o gear and have been in that range for a while. Tall torso, 29" inseam.
If you like the Wing, keep the Wing.
The FJR has decent weather protection, but it's not in the same class as the pre-'18 Wings and never will be. It is 300 lbs lighter than the wing. The Super Ten can be set up with ok weather protection, but it's not as good as the FJR. It has a more relaxed hip to knee ratio and more upright rider position. More neutral than the FJR's forward lean. Weight is essentially the same as the FJR when you add luggage to the Super Ten. Both can be comfortable, but there are techniques learned by the rider to maximize that too. "Sport-touring slouch" works well for the FJR.
We can't tell you what bike to buy, or if you should buy a bike. Only you know how you're going to ride it and what's important to you in the final details. Anything can be improved. Most bikes will benefit from a custom seat. The Wing may be the most comfortable stock seat. It also has a short stock range, compared to most of the liter plus Sport Touring bikes. Aux cells fix that for the Wing and other bikes too.
You can ride the IBR on any bike if you take the time to set it up well and learn it's ways, prepare for that and know the bike well. The IBR isn't a good standard for what bikes work well for LD riding. It just shows you that anything will do the job if you want it to. From Wings to HD baggers and including Ninja 250s & '70's vintage Triumph triples, it's a wide range.
My wife bought the BMW F650GS 2 for the '11 IBR. Prior IBRs had shown a tendency to have dirt road bonuses and she felt a lighter bike than her GL1800 would be a good idea since she sometimes struggled with the big bike on uneven ground. She was ~120 lbs and 5'4" at the time.
Then she got the rally pack for the '11 IBR at the rider meeting and found out it was a 48 state ride format. The GL1800 would have been much better for her than the little F650 for that rally. In hindsight, we should have ridden both bikes to the start in Seattle that year so she could have chosen which to use. It just didn't occur to us to do that after she had spent so much time, money and effort into prepping the F650. She would have had less drama with the GL1800, for sure.