Since I came around back to this, I probably should give an update:
Background:
I forgot which leak (Freak?), but Pokémon Black 2 and White 2 files were leaked. My understanding is that the files were similar to GitHub; a bunch of raw disassemblies, along the entire developmental timeline. To obtain a ROM from those file, one got to check out the files at the wanted phase within the development process, and to compile and build them into a ROM.
Among them, a "fes rom" was found; it was a way to distribute funfest missions via Local Wireless.
The original rebuilt game only appeared to work with other B2W2 debug ROMs. Unclear if this was an issue due to the revision or due to the way it was built, as another copy named "SWAN r59981 2012.06.11 [fes rom]" could communicate with retail carts just fine. fes rom is a branch from partway of the development timeline.
Observations (from what I could gather online):
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I think that's about it for now. I've not seen anyone try to share/load Funfest missions via a RAM hack or with a custom ROM (using Binaries not obtained from the leak), and I don't expect much development from looking into this.
The only other things I've seen are:
(1) the existance of an English patch (technically useless to us so not sharing), and
(2) unrelated to fes rom, it appears some missions were possibly meant to also be distributed as wonder cards.
Independant finding from theSLAYER and Eclipse
(Files from Eclipse: Berry Festival! (Funfest Mission).pgfGifts from Pokemon Center Women! (Funfest Mission).pgfEndless Battles! (Funfest Mission).pgfPokemon Quiz Championship! (Funfest Mission).pgf).
Reminder to not ask for any ROMs, not allowed here.