Hi Gabriel,
I'm glad to know you like the proof of concept. I'm sure that adding some basic features for improving function coding will boost productivity building REI3 apps.
As far as I know Ace has many of the features needed. Of course it's not a full IDE but REI3 does not pretend to be one. Focusing on functions as a way to add specific business logic to data model, Ace offers advanced capabilities to ease the code writing.
On the other hand it is fully customizable, with some useful extensions and no external dependencias. In addition the licence is enough permissive to be compatible with REI3.
Well, I have been using Ace for several years in other projects and works quite well.
For all the reasons above, it would be great if you consider seriously to integrate Ace or similar editor in REI3. I found a package for a native integration of Ace with Vue, but it's not official.
Anyway, If I can help with something in this task just tell me. Thanks for adding this feature as draft in 3.8 roadmap :-)
Regards.