Ruin Explorer
Legend
or functionally needs, as was arguably the case in 4e) an online reference
I don't think you can reasonably argue that 4E needed an online reference any more than any other edition. You didn't NEED any of that stuff to be online, and we've played plenty of sessions offline and not noticed.
But it was horribly useful. Like, I'd never play 3E again without something like that (which PF kind of has, actually, now).
I see it as a multi-step process. The first thing you do is a straight replacement. With some simple advantages like saving your changes and not worrying about losing the individual papers.
Then after that, people start exploring the capabilities of the device, and creating new things.
I strongly agree with this - just shifting the medium is a good start, and one that's already been done for a lot of games - I know our Fighter in 4E uses a strictly virtual sheet, for example, on his iPhone.