So I don't really have a concrete concept for this, but one attraction I'd really love to see at some point is an indoor boat ride in the vein of the mine ride concept:

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I think putting one in this part of RRR's land would allow them to add a major attraction without necessarily taking up all the space like a coaster:

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As far as the theme goes, I think some sort of lumber mill would fit. Have the boats look aesthetically similar to logs to give it a log flume vibe.
As far as the ride system goes, since the park seems to have a good relationship with Mack, I think a water coaster would work:

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Have an elevator lift at the end of the ride similar to JTA at SeaWorld San Diego, and have it drop about 6-7 stories as the ride's finale. I feel like as far as water rides go, building it mostly indoors would help with maintenance as well as increase the amount of time it can operate during the season.
As far as the surrounding area, bring back Frontier Outpost in the style of Forbidden Frontier at Cedar Point (large interactive area). This could easily be the most immersive area at Carowinds.