What Would You Buy If..........

Either Fuji GFX 100S...or Leica M11 (maybe even the Monochrom).
Lenses for Fuji: at least the GF110 f2.0...and then probably a nice wide angle or wide angle zoom.
for Leica: NOCTILUX-M 75 f/1.25 ASPH or the SUMMILUX-M 90 f/1.5 ASPH + (again) a nice wide angle....maybe the SUMMILUX-M 21 f/1.4 ASPH...well ok...I would have to add a proper 35mm ofcourse (the APO-SUMMICRON-M 35 f/2 ASPH would do very fine, thank you)

And that's all without money being an issue...which it still is ofcourse :-)
Depending on your M11 setup, LeicaMan, I could even go as far as to exchange my Sony gear for one of your M11 cameras + lens(es) :-)

I'd love to tinker with a new camera system, but it took me years and many a $ to figure out what Fuji lenses I like. Going through that process again on another system seems tedious, for the somewhat minor gains it will yield. I think I'd mostly re-buy what I have (Fuji+GR).

Although I would perhaps consider replacing my X-Pro2/23f1.4 with a Pixii, just to satiate my curiosity...

If m4/3 no longer existed, I'd have a hard time deciding on a suitable replacement. I'm not a big fan of the Sony lineup and Canon/Nikon's APS lens offerings are pathetic with no signs of improvement anytime soon. Fuji XF has some great options for ergonomics and lens choice so it's a strong contender for a physically smaller/lighter kit. My only real concern is whether the X-Trans raw files would cause issues in post-production. In the unlikely event I went with a 135 format camera, it would probably be a Nikon with a 2-3 f/1.8 primes but I'd really rather keep my kit smaller than that.

I’m happy with my Sony gear, but if money were no object I’d add a Leica Q2M for fun

At this point I have pretty much everything I want. My camera body is an APS-C Canon 90D and I have a selection of EF-S and EF lenses.

If I had to start over, I would basically replace the same gear I have. That would also mean an "upgrade" to mirrorless. The current APS-C Canon mirrorless cameras include a strong candidate, the R7. I would also get the adaptor to allow use of low cost EF-S lenses.

I would definitely stick with APS-C. I shoot some telephoto and lots and lots of macro, so APS-C provides some advantages there. Overall the added performance and image quality possible with a FF camera are only slightly better than results with an APS-C camera. The major difference is the cost of lenses. APS-C lenses at least from Canon are about 1/4 the cost of equivalent quality FF lenses. Trying to cut corners on the cost of FF lenses gives up an IQ advantage of a FF camera.

Sony a7rV (or the new to come a6xxx flagship depending on its specs) + FE 200-600mm.

I really like this a7rv review by the way, very straightforward, less bull.

You moved me so far out of the box in my crysis that I am not sure if the GAS kicks in again or I am just contemplating on my stuff again.
Well, I realized there is nothing holding me back to switch systems. Now, when this occured to me, I am not as sure anymore.

Canon: Milking it, RF system immature, good gear very expensive.
Nikon: Immature, I had previous issues with Liveview, UniWB, and other stuff. High res stuff expensive
Sony: Colors off, poorer quality (my experience), poor menus, overall aproach.
Other brands: brief experience (purchased) >> for my basic needs somewhat inferior, chaotic, not liked.
MF: eeexpensive and heavy.

So it is as with everything. There is no solution on the market that would truly fit my needs and made me happy. Now what! :-)
I am leaning towards sony. Great specs, available lenses, high res, affordable second hand bodies. I have been waiting for Canon five years, and they did not deliver. So there is no expectation of the future.

What say you? :-)
Can anyone support their choices with rational arguments "for and against"?

To read you in general, it's really not the photographic equipment that is the number 1 problem.
It's your perception that seems so negative to me. A break of several months or years would do you great good.
Forget photography, and find an activity that can lift your spirits.

Indeed, I am working on that. But it is not a momentary issue. This perfectionist approach is so engraved in me, that even with all these pauses, new views, "therapy" of such worldview, it will take time. In the meantime, one has to operate in that mode anyways. I cannot do nothing for years. I can make do, go by, ignore or accept these issues in ordinary daily routines and situations, but hobbies? Maaan it gives me trouble. Audio, Photography, 3D printing, sports. It´s just torture and hell. :-)

If the Ricoh GR series ends tomorrow I would truly be at a loss. I honestly don't see anything else on the market that fits into that niche segment of the market.