I will state here my personal view.
With the current AGE-engine used for AJE, it is impossible to have, anytime in the future, a user-friendly scenario editor. It will not happen.
Scenarios are possible to create, with the source xls DB files, of course (no estimated time to release them, sorry), but it is a very arduous and time-consuming task. ElNino and PhilThib are the Olympian masters that create all official scenarios for AJE.
Currently a very talented modder is working on a specific scenario for AJE, and he is working on it for months, now...
Regards