Yeah it would be nice.
But a couple of things, so Language Server Protocol (for those who don't know what it is) and also read
A Common Protocol for Languages.
And there look at the different
Related to Visual Studio Code you have 2 projects
So yeah you can have a language server that supports the AS3 language but written in any other language (C++, Java, C#, etc.)
Or you can have a language server written in AS3 to support the AS3 language (and maybe others).
And ideally with that you could either use something like Visual Studio Code or the Monaco Editor,
and a language server that supports AS3 and have a very nice cross platform AS3 IDE .
Personally I would rather write a language server in AS3 than something else (like Java),
and I do think Redtamarin is up to the task to either build the language server, and/or a SDK associated with it and/or tools associated with it.
I also think that an AS3 IDE could be build on top of Adobe AIR with an HTML view that reuse the monaco editor, just for the sake of saying "oh you think ActionScript is dead?, here an IDE build only in AS3!".
But I must admit it's not high in my priority list as for the last year I rather focused on packing redtamarin with features.
That said, I can help/contribute/participate etc.