I never went to this playground before my daughter was born, but now that I have a reason to go in there, I can say it's a pretty cool place and she loved it (she's not even two yet)! You would think a playground is the last thing you need to do at a theme park, but it comes in handy and kids have a blast! Just look at the splash park in NFL... I can see them keeping the playground area, but getting rethemed just because HISTK is outdated and kids young enough to play in there don't know the movie and probably have never watched it.
With a retheming, nothing is forcing them to keep the idea that you're shrunk; they're spending the time and money to retheme, so they can come up with whatever new theme they want. Thinking of some of the new Pixar movies that are coming out, they could do Toy Story, Cars, or even Finding Dory. Inside Out is also another idea they could run with.