Since it will be a LTS release, there are going to be three releases (main,
Edu, and Pro), as well as the planned Mini version. We have a lot on our
plates!
We keep a [http://trisquel.info/en/wiki/next-release-roadmap next release
roadmap] in our documentation. But mainly, we just follow all the updates to
packages that come from Ubuntu (minus all the non-free ones of course).
Like for 3.5, there will likely be a beta, then a Release Candidate, then
finally the release by early Summer.
Soon I will be posting a collection of artwork (bootup splash, wallpapers,
menu bar, and CD jacket art) to be used in 4.0 on the website
http://www.art4trisquel.org That should give you a good preview of the art
that will be in the next release (assuming Ruben decides it's good enough to
include, of course).