I've noticed that in 3.6, the Arcade editor has switched to some embedded version of what seems to be VSCode. This editor has LSP functionality for Arcade, but I can't seem to find any official published extension that allows for this outside the built in editor.
I know the integrated one has some context sensitive autocompletes, but I feel like even without those having an Arcade linter/LSP available in a normal editor would be very useful. Especially since I frequently track my Arcade in an external repository and currently need to use the less than ideal JavaScript language mode.