I did a little test, and with a language server one could do things like syntax validation, code completion, validation errors, document outlines and quite a lot more. As in full IDE support for archetypes without actually writing an IDE.
I have a very very small prototype that does rough document outlines for an archetype, plus it shows ADL syntax errors in the editor. If anyone is interested in actually doing this, send me a message and I can open source the code.
What a language server cannot currently do however, is highlighting code 
