Hit the nail on the head there, Chris.
Whilst it may seem easy to just look at whatever's popular in the media and build an attraction based upon it, there's going to be a large chunk of guests unfamiliar with the property who also want to be entertained, and don't want to feel alienated just because they aren't aware of the work it's based upon. This favours internal properties, as not only does it feel unique to the respective park, but if guests feel like they want more content, it's all there. They don't need to go home and do post-research on Netflix or whatever. It also means that a wider group of guests can experience said attraction together, instead of a group of die-hard fans of the property bringing in people who are unfamiliar, thus leaving them alienated.
And speaking of uniqueness- what's the chance that there might one day be other attractions with the same show attatched? This can easily be seen with The Walking Dead, with various parks across the world utilising the property, thus devaluing the ride at Thorpe Park. And sure- you could argue that there are other magic themed rides around the world, thus detracting from the uniqueness of Symbolica. But what makes Symbolica shine is that as Efteling have created the property of Pardoes, they have complete creative freedom, and can really make it their own thing.
You've also got to consider how many people will know the story, and if you're re-telling the original or simply immersing guests in the world of whatever it is you're adapting.
If you're re-telling the original work, you've got to ensure that it isn't changed too much and that it retains whatever made the original great. If you make a change, the fans are going to notice, and it'll probably stick out as a negative. For example, take the film adaptation of Les Miserables. There were a few occasions where the odd lyric was changed or an extra bit of exposition was added, and it felt really distracting and took me out of the world for a moment. So if they're re-telling the same story, they've got to be careful that it feels like a natural step-up from the original, rather than an "alternate vision".
Or you could tell an entirely new story, but this isn't without it's own set of issues. Whilst it's easier to sell to people unfamiliar with the property, unless you're collaborating with the original artists (which is highly likely), it's very easy to tell a story that doesn't quite feel at-home within it's respective world. You could take a look at the infamous I'm a Celeb maze at Thorpe Park as an example of how not to adapt a pre-existing work into a new story. It seems to be of common opinion that the experience on offer didn't represent the atmosphere or character of the show it was based on, leaving viewers rather confused and dissappointed.
There's also the issue of whether the story fits the type of attraction it's being built upon. Take The Gruffalo for example, from both a story and ride perspective. The story told on the ride feels wishy-washy as the transit wasn't designed for a "story-line" as such. Boats will be passing through each scene at varied speeds due to load, and as these particular boats are unable to be stopped/held, there's a really short amount of time to tell any story. Because of this, the story is incredibly easy to miss. I have a good understanding of The Gruffalo, but due to the way it was told on ride, it was genuinely confusing and tricky to grasp. If the same story had been applied to a different transit, say Tomb Blaster, the story could've been much easier to follow.
It's safe to assume that whatever ends up taking the Wobble World building will be a walkthrough, but even then that poses issues, as I've heard Room on the Broom has a lot of troubles with keeping it's audience captivated as the type of attraction doesn't fit the story they're trying to tell.
We can only remain optimistic and hope that this new attraction is something unique, but unfortunately it seems that the current future of the industry is based off well known characters, and it's such a shame to see. Whilst there are occasions where we get something brand-new and fresh such as Wicker Man, the general direction seems to be that of "more brands means more recognition".