Plymouth is still around and is used by Fedora, Ubuntu, Mandriva, and other Linux distributions as its boot splashscreen. However, there hasn't been much to report on now that Plymouth is fairly mature and there's not much more to get out of this booth splash screen that leverages kernel mode-setting for a clean and dynamic experience.
Plymouth hasn't seen a new official release since early 2010, but there's still new activity: about 200 code commits since this last release. In the Plymouth git repository there are commits from time to time, but nothing overly huge has been introduced in quite a while -- it mostly comes down to bug-fixes and minor enhancements (e.g. font selection for themes). The Plymouth mailing list is also very light. There has been some talk though of using Plymouth when Linux enters and exits its hibernation mode, etc. Simply put, however, there isn't much new activity in the land of Plymouth.