Something like Chiapas or Valhalla isn’t really possible under the direction/funding of Merlin. Building that much theming would be deemed a waste of money (Yes, WM has a decent statue, but has nothing else other than a few banners and wicker symbols, no landscaping etc).
Take a look at the new theming going on at Chessington for their log flume, a shell of what it used to be, with only one major addition of the tiger rockwork. It’s never warm enough in this country to build a water ride tbh, and unless they go out of their way to make it an exceptional attraction (spoiler: they won’t) such as chiapas, I can’t really say I’d want one?
I’m not fussed about them opening up SubTerra or Charlie, both are dismal excuses for dark rides, and are just not that entertaining once you’ve done them once. They do need more flat rides though. Enterprise and Blade are all thats left, and they’ve been part of the park for decades.
ATI, all of your “suggestions” are ridiculous tbh, none of them will happen. Rita isn’t going anywhere until it doesn’t work anymore, then it’ll sit SBNO for 3 years. A wing coaster would require too much height to be built at AT, the heavy trains mean that a layout is restricted in length without height, unless they went down the launched option, but I can’t see the benefit there. An RMC would be too “similar” to WM. We already have a terrain woody, that’s all you’re getting.
I’m not entirely sure what I’d want them to do next.