It is still not available in the official repositories but he's working on it. Meanwhile here is a link to his official webpage:
Here you can read on updates on the software releases and links to Sourceforge to download the DEB package.
This can download and install new plymouth themes from the official repos and it also give you an option to make your own theme. You can give it a try if you like to have a nice GUI for changing your splash screen. It's still a fresh software so expect a few things that will not work the way you want it. Just give a feedback on your experiences and suggestions to Mefrio. Give your feedbacks on this utility on the Ubuntu Forums http://ubuntuforums.org/showthread.php?t=1595812.