It's bad. Way worse than betacam, which was bad in the first place. You can't really remove moire in post. There are ways to mitigate it. But download that sample video in the 6D thread and try acceptably removing that in post. It won't happen.
And seriously look at 6D sample footage. To me it looks terrible, worse than the older generation, which had serious problems. That said, I own and operate a 5D Mark III and a C100 and the best footage I've shot has been on my old t2i and a rented 5D Mark II. So it depends on the project. For wide shots or for fabrics I think the 6D might be a small disaster, at least as bad as the 5D Mark II, 7D, etc. if not much worse. Just look at the sample footage. Does it bother you? If it does, don't buy it. No one else can make this decision for you.
That said, I'd get a t3i, used Mark II, Mark III, or C100 for video if you need Canon. Or a GH3. In fact I'd just get the C100. This camera is great! But failing that the GH3 seems to be the thing to get if you're not tied into the EOS system.