You guys are seriously happy with a half a sheet of paper?
I'm curious as to what you would use one of these for.
There are a lot of fields in which serious work involves reading full-page-sized layouts with ultra fine details like graphs and figures. For me, this is to read hundreds of conference papers and journal articles. But it's also relevant for any print in magazine format, heck even web pages. (Go ahead, claim scrolling around each screen is fun and efficient.) Other's have pointed out uses like musician's scores, larger displays, etc.
While even the iPad Mini now has sufficient resolution to resolve a full page detailed document, the human eye is not so able. In fact, it's really unusable. You have to understand that the iPad Mini 10", for all it's glory, is actually only the size of a half a sheet of paper. Compare that to an old fashioned newspaper that was 4 pages in size.
I'd NEVER want to use a 13" iPad for reading a fiction novel, but I'd also never want to use a 10" iPad for serious full page work. For now, I still literally have to carry print outs with me to read stuff when I'm "mobile."
To be totally honest, it's the 10" iPad that I feel has limited days at this point. It has a valid existence now because it's light, and a 13" iPad Pro will likely be too heavy at first. But once that goes, there's totally no reason for a 10" iPad -> it's just 20% bigger than a Mini, you can't hold it with one hand, and it's no more portable than the 13", which is the size of a full sheet of paper.
Remember - Steve Jobs experimented and found that 10" was the MINIMUM screen size you could comfortably do things on, not the MAXIMUM size. I've been begging Apple since the day the iPad was released to please release a bigger one - I called it the 14" iPad Pro, because I'd hoped it could be bezel free, and the size of a full page of paper. But weight is by far the important thing here - this is still something you hold. So that may hold it back a bit.
(As a related example, I have a 17" Macbook Pro because I do serious production work and can't count on an external monitor all the time. If I had a 13", I'd be reduced to email and web browsing for the most part.)