Yes, I am thinking of abandoning hope.
But you already bought the the back!

Exciting though my brief journey into the MF world has been, it has been very unproductive. In the last year and a half since I bought the IQ180 I've only shot about 1000 images compared to around 50,000 with my Canon gear in the same period.
Larger formats have a different shot ratio, I could probably unload hundreds of shots on my iPhone for dozens on my Canon to just a few on my 645Z. If I shot large format film, I'd probably happy with 10 photos a month - if that.
There are many reasons, perhaps the inability to shoot at ISO over 200 (even at that I feel there is too much noise), very old camera to go with it, lack of live view, need for a tripod most of the time, etc. I did spend a lot of time trying to get the most out of it but it has not been easy. I realized before I bought it that there would be challenges but I did not realize it would be that difficult. My fault, yes.
I was quite close to getting an IQ back myself a while ago, and a lack of high ISO probably wouldn't have bothered me too much as I have another system to fall back on, but for photography in controlled conditions CCD backs can look quite good.
Most of all I was disappointed with the upgrade policy. When I bought it I was told that the path to the next model would be very easy and relatively inexpensive. When I called a few months ago to see if I could trade in the IQ180 for the IQ250 (figuring I could put the high ISO capabilities to good use and then upgrade to the new camera body when it came out), I was told it would cost me over 20,000 to buy the IQ250 even at trade-in because it was being traded for a 'less expensive model'. Which meant that my $30,000 IQ180 was now worth less than $10,000 in just over a year. Somehow that did not make sense.
Don't know about your expectations, but I rarely buy any piece of electronics expecting to get anything resembling a good deal down the line, if it comes with digital components, I know I'm buying it for keeps. But if you do want to sell, only do it privately with other people, so long as your price undercuts the used prices of retailers, someone's sure to buy.
So I soldiered on, hoping I would be able to get more use out of my present system. Even tried out the 250mm SK LS prime, bought another lens (75-150). Paid $750 for repair of the shutter release mechanism on the camera body.
Sadly, I have still not been able to use it despite having traveled to South Africa and having done local tours in the US. The gear cannot replace DSLRs (at least not right now) and to carry both systems into the field is just too much.
As long as you keep your lens and accessory count rational, I personally wouldn't find it too difficult to travel with two systems, but your needs may be different. Of course it depends on what you want to do in your travels, sometimes you have to compromise and accept that you won't be doing landscapes, street photography and wildlife while traveling abroad and pick something to focus on.
Which brings me to the present. Given my experience with the Sony A7R, the news of the Canon 5DS/R and my existing multiple Canon bodies, is it worth it for me to hang on the MF system or should I cut my losses and sell it all?
Among the new high MP count cameras, the 5DS seems like the least exciting, unless Canon proves us otherwise in regards to their historically poor low-ISO noise/banding and DR performance. The A7R wins on size, but its noise is worse than the D810.
I am primarily a landscape and wildlife photographer, do not make a living from it and do not do portraits or studio work - other than family pictures now and then. While the results from the MF are stunning and the large prints I've made truly 'immersive' as they say, I am not sure that is enough to carry on with the system. I am not going to be able to get into the esoteric world of tech cameras at all, so further 'improvement' in my images is very unlikely.
As a landscape photographer you probably should have gone the tech cam way from the start, they're not nearly as large or heavy as I expected from pictures online, and in person I actually found them quite small. Perhaps your impression of MF not being for you is from having used it with the "wrong" system, the DF body is more for general use, and in particular, I find it to be a studio camera more than anything... The first impression it gave me was that it was just too slow and clunky to even bother taking outside, and the problem might be in that and not the back itself; even with a god-like sensor, a terrible body will still foul the experience.
I am not sure if I should wait for a CMOS version of the IQ180 - what if the trade-in is equally expensive? The new camera body rumored to come out in April will be no less than $5000 if that. Granted the lenses are great and would hold value for me, but that's about it.
Since the 33x44 CMOS just came out, I expect a full-size version will be at least two years down the line, but the manufacturing process is claimed to be difficult enough as it is right now. Concerning the new body, it's ultimately going to be just as large since the flange distance, prism and back configuration have to stay the same to retain compatibility with the current system, but if the operation is smoothed out and it'll be practical to hand-hold without strobes as the Leica S and 645Z are now, that would be a nice change.
Has anybody been in a similar situation. Are others thinking of jumping ship?
i just jumped ship from Canon to the 645Z, but I would have been happy with a CCD back too, if anything it would help me justify owning a $1200 tripod.
It is not just about the money (who am I kidding!), it is the whole experience I guess that has been 'difficult'. In my quest for the ultimate in image quality I may have indeed bitten off more than I can chew. I guess it is buyer's remorse a year later, I don't know.
I still think the DF is the problem, as of now if I had to put together a list of worst camera bodies in medium format, the DF+ would be at #1, followed by the Hasselblad H at #2. The 645Z I can hand-hold with the 55mm at 1/125th with fair certainty and at 1/200th I pretty much know I'm going to get a sharp image, while on the few occasions I used the DF I just couldn't get tack sharpness even at 1/300th, which was made more infuriating by the limited ISO as you say, but If the body had better handling and mirror/shutter action, and if the lenses had stabilization, it would be much more fun to shoot with.