You know what I would love to see in an episode? (Or even being the main focus of a two-parter)
I'm sure you all notice how the CMC look up to the Mane 6 as near perfect beings at whatever it is they do (Most of the time), and yet the viewer can plainly see that the Mane 6 are NOT perfect, and very definitely have flaws when they are interacting with amongst themselves, or some other sort of way that the CMC cannot see, or understand.
The interesting thing is that I think the Mane 6 also views Celestia in this manner. Heck probably every pony in Equestria does. It's almost as if they believe that she is awesome enough to not have to go through some of the hardships that normal ponies have to go through, both mentally, and physically.
Of course, as with the case of the CMC viewing the Mane 6 as perfect, this is definitely bollocks, and Celestia definitely has some sort of innate fear, or situation she would struggle against were it ever presented to her. It just hasn't been realized yet.
That's what I would like to see be a focus of an episode - seeing Celestia get brought down to Earth making the viewer realize definitively that she can be in as much a mortal dilemma as normal ponies. Even better yet, it should be a psychological one, which would be all the more intriguing. It would preferably be a season opener, or ender, because the act of bringing a god like figure down to Earth always has to raise the stakes in some alarmingly huge way.
One can argue that we already saw some of this in A Canterlot Wedding when she was beaten by Chrysalis. While it does bode true is some cases I don't treat as a "the" moment I want to see since this moment was more of a physical blow for Celestia, and it's been made clear that Chrysalis has been god-buffed already, so it takes a bit away from the feeling of seeing Celestia fall.