One piece of advice: for each of the suggestions, include a paragraph justifying why there is a need for that feature (and even better, links to forum topics by quest authors demonstrating that need). For example I see many items in the list that could be implemented, and be somewhat useful in some situation, but don't seem worth the time or added code complexity to implement unless there is a demonstrated need by quest authors, like octal support, function pointers, global arrays of object pointers, etc.

I also cannot endorse Saffith's comment above enough:
This is right at the top of the list of things we absolutely should not do. One of the big problems with ZScript is all the internal behavior it already exposes. Anything that's visible to ZScript has to remain in the game, or at least be emulated, indefinitely.
This is also one of the reasons for converting all the built-in objects to scripts: it would allow access to their inner workings without putting them forever off-limits.
One of the big mistakes we made in the time between 2.10 and 2.50 is adding many new features without fully thinking through what the consequences would be for future backwards compatibility and for future ports and rewrites.

I see several mentions of AngelScript. Is somebody working on replacing ZScript with AngelScript (I think LUA was also discussed in the past as an alternative)? This is an excellent idea. It may even be worth considering Python.