Nice!
The other issue is what occupies people's hands. It's surprising for me to see how many tourists use traditional maps (though, on the flip side, one never knows when someone is looking at a map on their smartphone), and how many people don't ask passers-by questions in order to get help. A dedicated app would mean less happenstance intereaction while abroad but it would also help not waste time (and give more time for more sights to see).
Another HN commenter mentioned offline capability, in this sense it could be like Wikipedia's make an e-book function, where you'd get, in the case of my idea, the pertinent street view photos, together with the right info downloaded to your phone. For ex, "give me top 10 comments on the Mona Lisa, 5 levels deep and for the Moulin Rouge, which I'm more interested in, give me the top 20 comments, 10 levels deep."
If a 'chapter' is to be added while on your trip, because you heard about something new and cool, then all that's needed is a wifi connection to download the right info and add it to the multimedia 'book'.