It's funny I'm a diehard horror fan and Halloween Is in my top 5 movies of all time for any genres, so the choice was a no brainer for me.
That said I can't help but think there is likely some people that would have interests in both machines. At face value they have very little to do with each other, but I think a lot of horror fans would also have interest in rubber suit Kaiju film's.
I've never seen Ultraman, but the pin looks gorgeous and ad someone mentioned earlier this would be very attractive to pair with a Godzilla.
I'm sorta rambling, but I guess my point is probably some fans would have bought both games if separate layout, and I'm sure a few may have even gotten both.
I like the concept of Spooky's approach here though, and hope it continues. One layout and maybe a more hardcore theme paired with a more family friendly theme. I'd love it if this might allow for more niche themes that might not be viable on their own. Like I'd love to get a cult horror film like Killer Klowns from Outer Space, or Hellraiser, Texas Chainsaw Massacre, the list goes on