Obviously a tablet this size would not be used the same as a small, portable tablet. I don't think there is a huge market for this but it would be really useful for some applications.
I can see this as a nice, interactive kiosk in an airport, hospital or mall. It would be great for some kinds of engineering and display of scientific mapping data. It would be nice working with an architect or interior designer or contractor to sit in an office and explore designs and colors and styles interactively on a screen this size or even larger.
This would be nice to have at a trade show to use to explain the features of our scientific software to prospects. I'd want it mounted on some sort of balanced extending mount like the old lamp style iMac display.
So, clearly not a portable device but using iOS on a large screen could be really good.