How i feel about competitive players and casual players in EDH: The competitive are german tourists, the casual are italian tourists, both in a italian beach. The italians asking themselves "why are the germans here?" make a legitimate question, the answer is because the beach is beautiful, no matter the country you came from. The italians wanting to ban the germans are dumb, because if the germans pay for their stay and follow the rules like everyone else, they have the right to be in the beach. Hovewer, if the germans started to ask themselves "why are the italians here?"... they would be dumb as hell.
I think making them acorn-only is the best choice and within the spirit of the whole MLP crossover, so they all can mantain the same exact aesthetic : silver border (notice they didn't either made them black border with acorn stamp exactly to maintain the same exact aesthetic consistency of the others), silly rules text, heart stamp hologram. Making them black border wouldn't make them playable inside a Princess Twilight Sparkle deck (the main reason they decided to finish this cycle) in any legal format anyway, and casual players will accept them even if they're not tournament legal. At least the acorn mechanics are pretty interesting so yeah, definitely approve this choice, I would make the same call.
I bought the previous ones and I'm glad these are silver bordered, makes them more collectibles than game pieces and not having to force them onto other players without an a-ok for silver border. If these were the norm for UB I'd be more okay with it, but with that said I'll buy this to finish off the set.