How is Apple going to react when you change the JSON (and thus the app, as seen by the user) without getting approval for the changes?
So I wouldn't be surprised if they react to that differently.
2.5.2 Apps should be self-contained in their bundles, and may not read or write data outside the designated container area, nor may they download, install, or execute code, including other iOS, watchOS, Mac OS X, or tvOS apps.
Older policy:
3.3.2 — An Application may not itself install or launch other executable code by any means, including without limitation through the use of a plug-in architecture, calling other frameworks, other APIs or otherwise. No interpreted code may be downloaded or used in an Application except for code that is interpreted and run by Apple’s Documented APIs and built-in interpreter(s).
Apple once prohibited a Commodore 64 emulator because it had a BASIC intepreter. But they've lightened up a bit.
It's definitely allowed for JS.
This looks like code to me, even if it is wrapped in JSON:
> {{#each posts}}
> {{# if ('type' in this) && (type=='stories') }}