Just a few counter points to consider.
Camera manufacturers will always need something "new and different" to market. They need to convince potential customers that whatever they currently have isn't good enough anymore.
That's true.
Full frame DSLRs provided the necessary hype for a few years, along with the quest for ever-increasing sensor resolution, video, and IBIS. All of these now incorporated into mirrorless FF bodies featuring a change of lens mount, that enables them to sell a whole new set of lenses as well as bodies.
I'm not sure this is "hype." There are real advantages and uses for higher resolution, video and IBIS. They aren't pretend features as the word "hype" implies.
...sooner or later, Canon etc will have to create another completely different line of cameras, and will have to convince us that they offer real benefits over what we currently use.
Over 60+ years the only "completely different line of cameras" that have earned widespread acceptance I can think of are digital vs film and now mirrorless vs. SLR. But in both cases, I would question how "completely different" they are than the cameras that came before them. I also question whether these were "created" simply to sell more cameras, as you seem to be implying. Rather, it seems like they were evolutionary changes resulting from changes in available technology. An "organic" change as opposed to one simply to sell new cameras.
Once we reach the point (5 years?) where hand-held pixel shift for moving subjects is truly usable, smaller formats won't be at a disadvantage, and their positive aspects such as portability and their greater suitability for computational photography will be promoted by the marketing folk, and we'll all be craving for APS-C and M43. There will still be a demand for FF, but IMO the bulk of buyers will be using smaller formats in 5 years.
That's one possibility, but I'm not sure I'm as confident as you are. What advantage would pixel shift/computational photography have for most enthusiasts. I am just one person, but for me, I enjoy the challenge of capturing a good image on my own, not through computer manipulation. Of course, I love improvements in autofocus, low-light sensitivity, etc., but having a computer "fix" my out-of-focus or blurred images might take some of the fun out of photography.
What I was trying to say was that I think the bulk of *current FF users* will switch back to smaller formats in 5 years time. By then APS-C will probably have reached 50MP, and AI firmware, in conjunction with merging of bursts, will have virtually eliminated noise and generally improved IQ to a level that matches the best of today's FF cameras.
For me, if full frame cameras reach into the 60-70 mp range, I don't think I'd have any interest in APS-C. I loved my 7DII at the time, but I don't have any interest in the R7, Mostly because I prefer the better autofocus and versatility of the R5. The problem with extreme crops that a 50mp APS-C camera offers is that there is a diminishing return because autofocus systems just aren't capable of accurately hitting the ideal focus point the further you get away from the subject. Perhaps that will change, but I'm not sure.
Novices on the other hand lack the experience or knowledge to understand what gear best suits their needs, and live in a youtube dominated world where people lack the patience to read written reviews and can't even be bothered to download and read instruction manuals. Many of them will ask a "photographer friend" for advice, but that advice is often biased towards the brand the photographer uses.
There are very few novices buying $2,000 plus lens and camera combinations as their first purchase. Most people start with an iPhone and then, if they get interested and can afford it, they progress up the ladder. That is a very small percentage of photographers and is likely to remain so.
The best way to advise novices is to ask them exactly what type of subjects they want to photograph, how much they want to spend, and then give them a shortlist of models from various brands, and suggest that they visit a store and try out each of them in turn to see which model feels most comfortable and enjoyable to use.
Where are they going to find a store to test these out at. Even Best Buy barely has any cameras anymore and brick and mortar stores are near impossible to find outside of major cities. Even Chicago barely has any camera stores anymore.
Also, I think that the popularity of lenses such as the RF100-400mm, RF600mm F11 etc clearly show that many people are fed up with heavy gear, and will increasingly turn to smaller formats. The R7 may well prove to be Canon's biggest selling camera... let's see where things stand in a year's time.
Have you noticed that the OM Systems OM-1 actually took 2nd place in the Imaging Resource Reader's Choice Camera of the Year 2022?
I think that's quite a strong indication of where things will be heading.
I would be willing to take your bet on the R7.
You may be correct about the desire for smaller gear, but I think that is more a function of the aging-out of the enthusiast base, rather than a reflection of new photographers. At some point, it gets too hard to carry the heavy gear.
Also, how do you know the popularity of the lenses you mentioned is because of the size and weight and not the significant cost savings. I suspect most people buying the 800 mm f11 are buying it because they could never afford the big white version.
Which also raises another point. The size and weight of the camera body is negligible in comparison to lenses for those shooting wildlife and birds. And, while crop sensors can allow the use of smaller lenses, I think most enthusiasts will still opt for the longest lens they can afford. The 100-500 on an R7 would give me more reach, but it's not going to make the combination significantly lighter or smaller.
Finally, since the older enthusiast base is also the market that has the most disposable income, they are more willing to pay for experiences that will get them closer to their preferred subjects and these "trips of a lifetime" offer a powerful incentive to carry the best equipment possible, since the cost of the equipment amortized over several trips is small compared to the cost of the travel.
I don't disagree with many of your points, but I don't think it is as clear-cut and simple as you believe.
