Setting project to "Wikimedia-Site-Requests" project as this request is about settings / configuration of a Wikimedia website.
For more information about how to request these kinds of changes, please see https://meta.wikimedia.org/wiki/Requesting_wiki_configuration_changes - this is missing a link to community consensus.
This extension is not going to be deployed on Wikimedia wikis, period. There have been numerous similar requests in the past, to enable extensions that essentially allow arbitrary code to be run on a wiki. It's just a security nightmare waiting to happen
Per Legoktm above, we have Scribunto/Lua for things like this.
If you need help implementing something to do this, and/or need more things enabling/exposing in Scribunto, please file seperate appropriate tasks
Why all public answers contain phrase "allow arbitrary code to be run on a wiki"?
It only looks like "allow arbitrary code to be run on a wiki", but in general, it works identically to Magic Words.
I agree it can be hard for security review because there are some hard coded parts that were written to provide better performance (and probably because it looks like "allow arbitrary code to be run on a wiki").
Second aspect is: it allows a lot of variants of code combination and it is hard to check them all.
I wrote more than a thousand tests and still not come close to this. Sometimes people send me bug reports when PhpTag stops working or does not return the correct result, but none of them was related to security issues.
Of course, I admit that there may be bugs that may lead to arbitrary code execution, so at each stage of running code, it examines the data that would minimize the risks. But unless someone can guarantee that its code does not contain such errors?