Notion rulesets were a good idea but there are many things they cannot achieve. It would be great if scripts could be written, with a focus, but not only, to affect playback, in a complete programming language.
If you vote for this feature, you are voting only on the above paragraph. Now I will state my preferences, however these can be discussed independently.
I believe the best syntax for such a scripting language would be Python's, however Python is too slow for this purpose. You should probably choose whichever language you think will be fastest between Lua and Ecmascript 6. Do refrain from creating your own language.
The documentation will require constant effort, independent from the release cycle of Notion versions. The feature will be useless without good documentation. Documentation on rulesets was not very good.