I am hoping they'll do something completely new for the next attraction, but it's likely that they will continue the theme of refurbishments/replacements. Flooded Mine has long been a candidate for complete refurbishment or replacement. They invested a bunch into Flooded Mine this year though, finally doing what was necessary to get the guns reworked and fixed a bunch of the moving props. Thunderation is needing TLC next. If they want to keep it, they'll need to work on it in a major way sooner rather than later. Sounds like it'll require a bit of ground-up work including support and track replacement.
I know I'd like to see more major indoor attractions, but it may be a long wait for the next one, unless they are blown away by the response to FITH and the lessons learned while building it.