For years there has been talk about turning Ubuntu into a rolling-release distribution, but previously nothing has materialized beyond some mailing list discussions. There's also been discussions of Ubuntu on a monthly release cycle, but again, it's been mostly all talk.
In January was more serious talk about Ubuntu moving to a rolling release model. Leann Ogasawara, the Kernel Team Manager at Canonical, talked about moving to a rolling release model for Ubuntu 14.04 LTS. She said it was "in the cards of possibly happening." It would involve eliminating the interim releases and only putting out the Ubuntu LTS release builds every two years. New packages would be pushed out after they are released and have cleared QA.
Now today on the Ubuntu developers' mailing list, Rick Spencer of Canonical is again talking again seriously about Ubuntu as a rolling release. His reasoning for Ubuntu as a rolling-release model seems mostly about conserving resources. Canonical is investing a lot into the mobile space -- and to some extent betting their future on it -- and by getting rid of these non-LTS interim releases, they can focus more on their mobile efforts.
Rick began his mailing list message with, "Ubuntu has an amazing opportunity in the next 7-8 months to deliver a Phone OS that will be widely adopted by users and industry while also putting into place the foundation for a truly converged OS. To succeed at this we will need both velocity and agility. Therefore, I am starting a discussion about dropping non-LTS releases and move to a rolling release plus LTS releases right now."
By eliminating the non-LTS resources the load of Canonical employees would be lightened as they don't need to support multiple interim releases simultaneously, don't need to worry about releasing every six months, etc. Canonical's paying customers also really only care about LTS releases. It's also acknowledged that some features currently introduced on the Ubuntu six month cycle are less than baked.
Rick even proposes that Ubuntu immediately changes its release model. "In the meantime, with Ubuntu Touch, the Phone, the Tablet, and convergence of these device experiences with the Desktop, we are in the process of inventing what is essentially a next generation Ubuntu. There will be lots of new code written and code integrated from new sources to accomplish this. The 13.04 Desktop would not have any of this new code, and therefore will be "old" before it is even released. Therefore, I think we should keep LTS releases, but tarting now, stop doing interim releases and start a rolling release."
Aside from daily development snapshots, Canonical would be putting out monthly snapshots of the development release that they would support until the next month's release is available.
It seems that this monthly cadence with a rolling release might really take off this time and does have the backing of several Canonical developers. Read more in this mailing list post