I took this to its logical conclusion with Topic List Previews Theme Component.
This used to be a plugin, until some of its functionality was adopted by Core (thumbnails) at which point I was able to put most of its functionality into a Theme Component to give it a bigger audience and an easier install.
I’ve added and kept some advanced features that require changes to the back end in a complimentary plugin.
Another good example here is Guest Gate Theme Component. This started life as a plugin, but turns out you don’t need it to be, so was reborn as a new Theme Component (plugins predate Theme Components).
There are probably still one or two plugins that could be converted into a Theme Component (I can think of one of the top of my head) … and there are likely to be more candidates as more functionality is added to the core API …