so on the basis of viewfinder pixel density a screen the size of the iphones could conceivably have 25 times as many pixels (about 35 megapixels or about 7000x4800 pixels!!).
It doesn't work like that, and you misunderstand the specs of your camera. The viewfinder has 1.4M
dots equivalent--not pixels or even pixels equivalent. The actual pixel count is much, much lower, irrelevant to the main LCD monitor on the camera, and certainly irrelevant to the iPhone.
On the basis of a typical desktop computer monitor density, a 60" TV "could" have eight times the resolution of 1080p. On the basis of your viewfinder, it "could" have well over five hundred times the resolution of 1080p (if your viewfinder
actually had 1.4MP, the TV "could" have over 1400 times the pixels). But it can't. We have no way of mass producing such panels at any price, let alone one that anyone could afford.
Making a viewfinder at a certain density with acceptable yields is very different from making a larger unit with the same pixels. Cost increases exponentially with pixel count, and QC-passing yields drop in an equally nonlinear fashion.
so I fail to see why a similar resolution on the iphone would even spark debate.
Because it
does not exist.
The new larger Rez screen probably costs now what the first iphone screen cost in 2007.
No, the higher resolution screen will absolutely cost more than that. Prices have not fallen much, if at all. That's not really the point though. The question is what supplier will be able to provide such a display. Postage stamp sized screens for niche markets have absolutely no bearing on what can be physically manufactured in volume at 3.5-4", just like your cell phone screen has absolutely no bearing on what can be manufactured for your laptop, just as your laptop has no bearing on what can be manufactured for your television.