I think Mark Shuttleworth answered

“In the work to underpin a rolling release, we made huge strides in automated quality assessment and performance testing.

“From here on our, I’m going to treat the cutting edge of Ubuntu as a rolling release, because the team have done such an amazing job of making daily quality a reality. That’s a value that we have all adopted, and the project is much better off for it,” said Mark Shuttleworth on his blog.

This means that users will be able to treat the daily builds of Ubuntu 13.10, for example, as a rolling release model. It may not be the best idea, by Mark Shuttleworth thinks that the quality provided is good enough.