In regards to it being a private contest:
I was asked to make a thread on MotK and I have permission from Overlord Helolpolis. I don't see any reason this contest shouldn't be open to everyone, though if you can think of a reason feel free to share XP
In regards to Junko:
It's just a silly plot point, don't think too much about it. Only, like, 3 of Junko's official patterns follow these rules, but that's not the point. The point is to make a beautiful and fun pattern even with restrictions and less flexibility. It's along the same lines as that one "you can only use lasers" contest. Yeah it's harder, but that's the point.
And just for reference, a surprising number of complex official patterns fit the criteria here. See: Aya's nons, Satori's nons, Mamizou's nons, Ringo's nons, Hecatia's nons
In regards to PhantomSong entering:
Why wouldn't you enter you definitely should!!!!