Excellent points. I've previously thought through most of them on my own, but my answers probably won't be the same as anyone elses.
The reason the back is attracting such attention is that is the first affordable way to get into 617 unless you crop 5x7, and unlike 612, the first practical way to carry 4x5 and 617 capability together.
I don't go out and shoot 617 (because of the equipment cost), but I have been with folks who do and yes, I would go out and shoot 617, especially if I could also do 4x5. The reason I haven't and wouldn't choose a Fuji/Linhof system is that a 3-lens set on these cameras run $8,500 - $9,000 grey market, so if the Canham RFH cost doesn't make sense, these cameras are total insanity. Not to mention the Gilde that starts at $6,500 without a lens, about $15,000 for the high end body and 3 lenses. The 617 RFH cost is not all that much higer than a decent 612 back, and the formats look quite different to me.
I'm not really sure the format is more situation dependent, and this is a very thought provoking comment. I think the format is better suited to different compositions, but whether those compositions are more or less frequent is probably in the mind of the photographer.
A 617 back has several advantages, but only the buyer can decide whether it's worth it. 6x17 is the standard for stock, so if roll film is what people expect, that's what you give them. More film types as you stated. Better portability over 5x7 holders. I don't see precision decreasing any more than any other RFH on a 4x5 unless the back turns out to have film flatness problems. If I wasn't interested in shooting 617 fairly often, or only for myself, of course cropping 5x7 makes much more sense.
You also gain movements, no lens cost, any lens works that did before, and critical focusing of a gg, although you do lose the convenience of the scale-focusing viewfinder cameras. You also cannot carry a 3-lens Fuji/Linhof system with 4x5 system at all. With a RFH, I can carry it as far as I need, probably a couple of miles or more.
Does it get heavier? Sure. I use 4x5 quickloads/readyloads, so I'm only carrying 1 film holder anyway, and think I can add a 2-lb back without killing myself. I also use a real backpack - a Gregory Forester - that carries weight much more comfortably and only weighs 5.5 lbs empty compared to 12 lbs for the big Lowe Pros. There are lots of ways for me to save weight, including the best way, losing some of my own!