I love the OHC format, but I can't think of anything that would definitely sell in that format... Irony!

Maybe Warren Ellis's three Astonishing X-Men arcs could be in a single OHC? I'd definitely buy that.

I'd buy a complete collection of the four Spider-Man's Tangled Web TPBs - these have a ton of great creators, but the "anthology" feel might hurt this, like Ultimate Marvel Team-Up.

I'd buy Brubaker's Captain America in OHCs, but I doubt that would happen since there are already Omnibus HCs and Ultimate Collection TPBs.

Since the PAD X-Factor is in TPB (and the original issues can still be had for less than cover price), and the Ladronn Inhumans was in a recent FF PHC, I doubt these would get an OHC anytime soon.
(They sure would look cool, though.)

Mike Hansen, The Geekiary & All Day Comics