I don't hold out much hope for an intelligent "hard mode."
I base my low expectations on ANet's existing practices. DoA is a boring hack-and-slash slog; I can do it, have done it, and find it boring as heck. Sure, DoA is "hard", in the sense of "hard work." Fun, it is not. I doubt more than a very, very tiny minority of the popuation plays in DoA, simply because it is often empty.
Forcing people to use PuGs will mean I have no interest in "hard mode", given the paucity of good players available in many areas for playing "normal" missions. Heroes have *SAVED* many mission areas by eliminating the need to spam "GLF" for hours on end.
What would I like to see? Revisions to the missions, adding additional objectives and monsters with complete skill bars and secondary professions. Better rewards for more challenge.
What we'll get, though, and level 28 Charr in Surmia.
Pessimism? No. Just look at how ANet has increased "challenge" in the current game.