Unpopular opinion: I think there is potentially a market for this, if they "own" their downmarket status. Still a fair number of tourists looking for a deal in that I-Drive area, and Orlando has gone from a podunk even as late as 1989 to a top 25 US city. That's a lot of locals, many of whom are priced out of WDW unless family gets them in, and who keep watching prices climb at UOR as well. (Reminds me of a conversation at HHN the other night--how do you sell $10 beers to a crowd of 20-somethings who barely make over minimum wage.) A reasonably priced alternative* could find its niche.
Six Flags has been rumored forever--a year or two ago they were supposedly looking at Boardwalk & Baseball--but it seems to me their main competition is the idea of Universal as opposed to Disney. Thrill rides and a superhero land sounds like UOR before Potter. I think Six Flags would go a little further away geographically--realistically, southwest of Disney, or maybe Volusia. Or wait a few more years for Sea World.
Know very little about Dollywood, etc., but could probably go with a Florida cracker/swamp theme or even just a wild West theme and do well.
Whomever it is, I think this backs up the general thesis of the Attendance Decline thread: Disney theme park and especially hotel prices have climbed too high. The industry smells blood in the Orlando waters. Ironic that TWDC spent billions on "blue ocean" development only to face a redder ocean than ever.
*Full disclosure, only non-Orlando park I've been to in my adult life was DisneyLand, so I could be off here on pricing. But I can't believe those places get $100/day.