14 DAY TRIAL // Things have been rather quiet on the Ubuntu 15.04 (Vivid Vervet) front, but that is about to change. The developers have already implemented Linux kernel 3.18 and they are also tracking the Linux kernel 3.19.x branch.
The development cycle for an Ubuntu version takes a little less than six months and the next edition of Ubuntu, also named Vivid Vervet (a funny-looking monkey, don't ask why), is scheduled to be released in April, so there isn't much time to implement a lot of changes.
Even if Ubuntu 15.04 will probably be a lot more similar to Ubuntu 14.10 and 14.04, it's pretty different from those two because the devs have already made some important upgrades to the GNOME packages, like Nautilus, GTK+, and a few others. It's likely that they won't stop right away and that we'll see some more changes soon.
Linux kernel is the core component
Ubuntu is a Linux distro and the kernel is a core component. It's important to know what version will be eventually implemented in the final edition of the distro and it looks like the 3.19.x branch is the lucky one.
"Both the master and master-next branches of our Vivid kernel have been rebased to the v3.18.1 upstream stable kernel. We have also uploaded our first 3.18 based kernel to the archive (3.18.0-8.9). Please test and let us know your results. We are also starting to track the v3.19 kernel on our unstable branch," said Canonical's Joseph Salisbury.
The next Alpha release in the series, for the flavors, is scheduled in a couple of weeks on January 22 and the Beta 1 freeze should land on February 22. If you want to test Ubuntu 15.04 right now, you can download it from Softpedia. It's a daily image and it's updated regularly. It's not stable and it can cause problems, so don't use a production machine.