This new spin alongside Ubuntu, Kubuntu, Xubuntu, Ubuntu GNOME, Ubuntu Studio, etc, isn't expected to have any formal releases at this point, but would be a flavor for developers and early adopters to experiment with the next-generation Ubuntu software being brought from Ubuntu Phone/Touch over to the desktop.
This new spin comes after repeated delays to the roll-out of Unity 8 over the past year. All we know right now is that the new code should be ready by Ubuntu 16.04 LTS -- in two years -- for the Ubuntu desktop. Having a new Unity 8 experimental flavor would make it easier for those wishing to test out the new code without first having to install the Unity 7 + X.Org based Ubuntu 14.10+ and then install the latest experimental packages from a Personal Package Archive.
Ubuntu's Unity 7 won't live on forever, but this is just a safe precaution to keep happy Unity 7 users content (and those seeking a stable Linux desktop) without prematurely pushing out Unity 8. Iain Lane, one of those organizing this new Ubuntu flavor wrote, "We still plan to migrate pieces of the current desktop over, but we are very mindful of the need to not destabilise the desktop and upset its users, and are hopeful that developing this flavour in parallel will mean that migrations will truly happen when software is ready instead of as a result of pressure to get work into the hands of users early."
More details can be found via the Unity 8 flavor announcement that was made this afternoon to the ubuntu-desktop list.