Themes are all well and good but even on the PS3, I've always found myself eventually going back to the default one. If they decide to add it later then fine, but there's plenty of other things that can add or improve first. I guess it all hinges on whether they made enough money selling themes last time round to justify it.
Same with me on my PS3 always back to the original, but what they do need to do is come up with a better way to manage the home screen on the PS4.
As every app, game you install seems to end up on this big long line that from what I can see you can not sort, or stick games/apps to the start
Kimbie