I used it with plex (in kodi) just fine. With that said, I'd agree that its mostly for local media (where local can be whatever plex can get to). Outside of plex, either you are using plain kodi or some simple kodi extensions (say youtube) that just aren't as nice to use as their android app equivalents (in regards to streaming services, it does support MLB.TV for those that like baseball, but again, not quite as nice an experience IMO as the android app).
Him, I hadn't tried running it myself, but I couldn't find any indication if anyone using it for Plex (or equivalent). I only saw people going thru complicated schemes to Terry and setup network shared drives, or directly attaching external harddrives. I stand corrected.
If my entire world was plex, I probably would have kept it as my main device, but I really like a lot of the android streaming apps i use and the experience in kodi land just isn't as good when it exists.