There's nothing that I saw in iA that I couldn't get with more functionality with vim or SublimeText and some LaTeX, syntax analysis, and Markdown plugins. There's also equally nothing in Writer "Pro" (attaching Pro to the end of a consumer product seems to be all the rage these days) that seems even remotely more useful than the previous iteration. It's a simplistic and stripped-down editor that has a nice typeface and color scheme, but why does it cost $20? There's no advanced story organization features, there's a very rudimentary tree functionality for branching by headings, but you can't jump to a heading, branch them into subtopics, attach object names to them, or anything cool like that. There's little distinction between the 4 modes, and I don't see the value in not integrating the features into only 2 – writing and reading. Most people don't write drafts, edit, and then edit more – they edit while they draft, and then perform several revisions instead.
The syntax analysis looks pretty neat, but for those with above-average vocabularies and half-decent grammar, it doesn't seem to offer anything truly revolutionary.
At least not revolutionary enough to sell a million copies, and especially not at the price they're charging.
However there's something about emacs that keeps it from being sold as a viable consumer product...
[0] https://github.com/bnbeckwith/writegood-mode
Update: added example link