I first mentioned this on the ubuntu-hardened mailing list in October.
As I mentioned there, this move will have several benefits, including the security notices being easier to find, more obvious linking to and from other Ubuntu security info, and staying in sync with the look of the rest of ubuntu.com.
Most of all, it will allow easier searching of security notices. Here’s a sketch of the main page:
(At the moment engineers aren’t keen on implementing the package search field, so that may not appear in the initial version.)
And here’s a sketch of an individual security notice page (Discourse shrinks it, so you may need to view it standalone):