Sorry for my harsh reply. It's just that I still don't see how a pen would help doing this on the go. Either it's a matter of normal typeface, in which case an onscreen keyboard being operated with fingers would be enough. Or it's actual handwritten text, in which case there is no way this can be adapted quickly, since the flow of the lines is very critical and should be done under calm circumstances.
Or do I miss something here?
I'm not a graphic artist, so perhaps I don't understand your workflow. My point is basically this:
Smartphones are so powerful that people are now using them for many tasks they used to do on their computer. They don't replace your computer, but they can supplement it for many tasks. Over the years as our smartphones have been getting more capable we've seen people perform more of their daily tasks on their smartphones.
So I see high-end software (like Photoshop) coming to the iPhone. Not because people will actually try to create content (or do other heavy lifting) on their iPhone, but so they have the ability (when required) to perform some basic tasks when they're in a bind or not near their primary computer without having to use some gimped "lite" version.