It seems like the offline bundle is for Ubuntu 12.04 (exact), which is a 4½ years old release. Are there any plans to do offline bundles for newer Ubuntus like 15.04, or perhaps just the latest LTS 14.04?

I know 12.04 is still maintained, but that doesn't really matter much on a machine that never connects to the internet anyway -- and building a new cold storage, I would naturally go for a newer release, not download a release from 2012. But perhaps that's just me :-)