As explained in the wiki article LTS Enablement Stacks,
The Ubuntu LTS enablement stacks provide newer kernel and X support for existing LTS releases. These can be installed manually, or are automatically shipped if installing from 12.04.2/14.04.2 and newer release media.
As shown in the chart below, newer hardware enablement stacks become available as 'early preview' (EP) a few months before the next point release.
The note in the chart says
Early preview of the HWE kernel being introduced in the point release will be available in the -updates pocket.
What is the '-updates pocket' and how do I opt in to it and to EP of LTS Enablement Stack?
If this operation is reversible, how do I opt back out?
Here's the details of my current situation, but I would really prefer this to be a broader question, applicable at least to all versions of 12.04 and 14.04.
I'm running a 14.04 LTS, installed and updated from 14.04.0 netinstall (Ubuntu 14.04.2, kernel
3.13) and I'm interested in trying out an Ubuntu 15.04 (vivid) and later kernels as they become available in Early Preview; especially an Ubuntu 16.04 kernel - because the support for older updated LTS enablement stacks ends the moment the new one becomes available, I figure it's good to try newer stacks in EP mode.