@Lyichir I hope you’re right, because if Hasbro’s involvement would serve to prevent a new theme’s creation then there’s no fear of an Equestria Girls mini-doll theme.
I would love My Little Pony and/or Equestria Girls sets (go Sunset Shimmer!), but that's one we definitely know would never happen, because the My Little Pony brand is wholly owned by Hasbro (unlike something like Star Wars that's based on an outside license). I think the toy industry would have to be rocked to its core for LEGO to even think about entering into licensing agreements with Hasbro or Mattel. With what big competitors they are it'd be too much of a conflict of interest.
A wave being exclusive to one retailer in a particular country is somewhat common for a theme on the verge of retirement, though it doesn't always indicate that… both Technic and Speed Champions have had waves that were exclusive to Toys 'R' Us in the United States.
While Elves is one of my favorite themes and I'd hate to see it go, I also think the fact that it got a fourth year is pretty impressive, since I had similar fears about LAST year. And this year's big showdown between the forces of good and evil would not be the worst way to end things (it certainly has some nice continuity with the introduction of the shadow world last year).
Here's hoping that if Elves does end after this year it gets replaced by something just as fantastic. Maybe something sci-fi even? I'm not sure how much precedent there is for girl-targeted sci-fi toys but now that we've seen modern-day and fantasy themes with the impeccable level of beauty and detail that LEGO puts into their girl-targeted themes I would love to see how that could apply to a sci-fi context. Overall, as long as the designers behind LEGO Elves are still creating exciting new designs I am optimistic about the future.
School starts back tomorrow, but in the meantime I've spent most of today working on this. If I can finish it, it'll almost certainly be my largest MOC since I was a kid. Certainly my largest constraction MOC.