1080p at 60fps would have likely made me an instant buyer. Even 1080p at 48fps would have been a major step towards instant buyer. Not sure what the hold up to offering these features really is - I don't believe it's only technical... I do appreciate the ALL-I recording format, like the 5DMk3 offers. That alone is a significant step of an upgrade compared to the Rebel line.
ALL-I is worthless and offers no improvement in image quality whatsoever, what do you like about it so much? And do you shoot that much slow motion that lack of 60P is enough to keep you from buying an otherwise much-improved camera?
shooting b-roll in 1/2 speed would be great to offer for some clients in a smaller/cheaper/portable camera. even if it were only a 10-12 second "burst" style mode that would be a great feature to have, when needed. and no, I don't shoot 1080/60p for everything and have no desire to. much prefer 1080/30p over 720/60p for that matter as well, and not just because of resolution. don't do a TON of slow motion work, but that's mainly because it's not offered in the camera bodies I regularly use. having the option would open some creative, in-budget options for clients - that's all.
I've had clients ask to shoot in ALL-I mode on the 5DMk3 before. having the option is great to be able to offer on a crop body, when needed. some stock houses and broadcast ONLY want high bandwidth files, regardless of the visual improvement or difference (and it's not the magical 50Mbps 422 that they really like to see). if this opens the door to more channels of revenue or opportunity somewhere down the line, then that's great for all who use it.