There's nothing stopping a community member from doing that, I don't think. 
I'd guess that staff would be less willing to showcase community apps, however, lest they seem to "play favorites" (or imply official support, etc., which they do not provide). That would leave them with the built-in apps, of which there are probably a few dozen, but maybe half of those are just integration apps you'd only use if you already have a reason to or want to use that service (Hue Bridge, Alexa, IFTTT, etc.), so not super-exciting for showcasing.
So, then we're left with only a few apps and they'd quickly run out of things to showcase until something new and shiny comes along. And when that happens, they usually do show it off:
So, some of this is already out there, maybe just harder to find if you don't know where to look. The Release Notes category is generally good to look at, or other announcement threads that are linked to from these.
For community apps...less clear, though if you pose a question/problem in the forums and someone is aware of something that might meet your needs, you'll usually hear about it. Again, someone certainly could create some specific community showcase--just a matter of who is willing to maintain the effort and whether people will utilize it, as a couple things have been tried in the past.
