Encountering "themed" gyms in Pokemon Go

In Pokemon Go, one of the game mechanics is that you can fight in "gyms" against pokemon that belong to players from other teams, or else put your pokemon in a gym that your team controls to help defend it. You get some in-game currency based on the amount of time your pokemon stays in the gym. Gyms can hold up to six different pokemon, and they all have to be from unique players and unique pokemon -- you can't put two of your pokemon into a gym, and you can't put a second Bulbasaur in there if there's already one Bulbasaur defending the gym. Different people have different approaches to decide which defenders to leave. Picking pokemon that are good at defending against a wide variety of attackers, like Blissey, is one approach. Personally I've gotten into the habit of leaving behind pokemon that I evolved in order to get the XP for evolving them but don't have high enough stats that I want them as permanent parts of my collection (so I don't have to worry about holding on to items to revive and heal them after they get knocked out of the gym by another player). Sometimes you also see people leave rare or exotic pokemon in gyms, such as the exceedingly rare "shiny" variants of regular pokemon, probably as a way to both spice things up and also show off that they have them in their collection. Sometimes, though, you'll encounter a gym that was almost certainly put together by a group of people according to a specific plan, like this one I encountered this morning:

That's the three different evolution stages of the electric-type pokemon Pikachu (baby Pichu, Pikachu, and Raichu) wearing the witch hat that you could get by capturing/hatching/evolving these pokemon during the Halloween event, plus the somewhat-recently-released gen 3 electric-type pokemon Plusle and Minun, which are generally restricted to being caught on opposite sides of the world except during special events. Seeing things like this brings a smile to my face, and even though this was a Team Instinct gym and I'm Team Valor I couldn't bring myself to knock them out of it.

I've seen some other interesting "themes" during my time playing the game (although it didn't occur to me to take screenshots of all of them). Once, before the gen 2 launch, I encountered a single gym with all the region exclusives that were available at the time: a Tauros (from North America), Kangashkan (from Australia), Mr. Mime (from Europe), and Farfetch'd (from Asia). More recently I encountered a gym with an Eevee and all of the eeveelutions: a Flareon, a Vaporeon, a Jolteon, an Espeon, and an Umbreon. It's a little bit easier to achieve some of themes in a distributed manner, like all pokemon of the same type, or the "all pink" gym with Blissey, Chansey, Clefairy, Clefable, etc. (if I ever see a partially populated Valor gym that seems consistent with a particular theme I try to pick a defender to add that will keep it going).

Generally I'm a pretty anti-social player of Pokemon Go, but it's cool to be able to encounter things like this in the game. (It's also easier for people to do this sort of thing with more and more pokemon, and more event-specific variants, available). I've heard some talk that there's going to be some sort of "quest" system implemented in the game (beyond just the "first pokestop of the day" kind of thing). Even though I'm not a fan of Niantic's focus on "social" stuff to get players to play in groups, I think it would be cool if the quest system resulted in some more distributed interactions that had impacts like this -- if you had a goal like "have your team control gym X with 6 fire-type pokemon" you might not need to travel around with a group of teammates to knock down the gym, you might be able to just have people independently trying to hit that goal end up achieving it. You could get that "hey, neat, other people are playing this game, too" feeling without explicitly finding particular people to hang out and play with.