Joking aside, I predict disappointment. Reddit users will want hard-hitting answers, Obama will definitely not give them (already the internet freedom question has been fluffy-answered). In all honestly, no-one should expect anything else- the POTUS is not going to unveil new thoughts and strategies through Reddit.
That said, it shows how far they've come from the "jailbait" scandal a few months ago, but I strongly suspect Republicans will refer back to it in good time.
EDIT: Hey, at least PresidentObama bought Reddit Gold. Somehow I doubt it'll be enough to cover the bandwidth, though.