Okay, I probably know the answer based on prior experience with it being a pain to go back and forth between InDesign versions, but I have to ask:
Will InDesign CS6 users be able to open InDesign CC documents and go back and forth easily between CS6 and CC without using the IDML format as an intermediary?
Probably not. *Any* new feature in CC would make that impossible -- even though it's as little as a single new object (QR Code comes to mind; the "other" improvement, a Dark UI, cannot be transferred).
(Even if it's *technically* possible, why'd want Adobe support this? People then would not have to buy/subscribe to their new cloudy subscription scheme!)
The answer is no. Same IDML workflow will be needed.