There haven't been any significant updates to PlexConnect for quite a long time now. The github page only shows minor updates for the past few months. Are the devs waiting for Apple to release a new ATV and hopefully an app store for the Apple TV? Or is it because PlexConnect is working very well now and doesn't require frequent updates?
I think it is more about the fact that Plexconnect is now at the point where it is working and there are no major requirements to be developed. The small changes you have seen are to do with Bug fixes or other suggestions.
There had been other people working on Themes etc, but as these all are a little more complex to install and get working (requirements for Pil or Pillow to start with) the main developers have not merged these changes in.
I ma sure when more is known about the next ATV and if a "App Store" is available we may see more activity as they make it all work in that situation.
I would say that anyone keeping a keen eye on updates to the changelog from Baa and the gang should try out some of the offshoots of the original version. I love the brotuser and falco953 project that lead to fanart population and a more animated/single click to access your content - style of layout.
All in all, I would agree that PlexConnect for the most part is solid, and really has become the best of it's kind. Tweaks, roadmapped ideas, and community recommendations would certainly be in all our best interest, but it's legitimately less pressing now. I think, anyway.