Will the App Store reviewers allow scripts downloaded as text, if it is parsed via WebKit?

Apple's review team will reject your app if it looks capable of downloading executable code. They have erred on the side of rejecting apps that legitimately look like they will only even "interpret" the code since Apple stands far more to lose when third parties discover this path to executing code and inject the code between your web server and your app.

The stakes are too high - so you'll want to be very careful that you understand the risk to your app if you include this functionality.

The briefs app - which was submitted to the app store in Late 2009 I believe, was hung up in this "what is the difference between interpreted code, downloadable game data (think new levels for a game), executable code" review state until April 2013

• http://blog.robrhyne.com/post/659211315/almost-on-the-app-store
• http://iphonedevelopment.blogspot.com/2010/08/briefsapp.html
• Wireframe iOS design apps for iPad?

Clearly, there are far more apps on the store that use interpreters so your path to approval is likely to be smoothed by the efforts and pain of the pioneers that got Apple used to the idea that they can ensure interpreted code and configuration doesn't turn into executables.