It would be interesting if Figwheel could essentially decorate any implementation of IJavaScriptEnv, taking on the responsibility of watching the filesystem (perhaps even delegating that to ClojureScript :watch, and expanded :watch-fn, and perhaps minimally calling IJavaScriptEnv -load when Figwheel determines it is needed.
Then, for those REPLs that can participate, if IFigwheelSupport can be extended to them, they can do further cool stuff. (Perhaps IFigwheelSupport is actually necessary while IJavaScriptEnv as described in the previous paragraph is insufficient, and a more fancy impl of -load is needed?)
That way, things like the existing Node REPL could be minimally supported by Figwheel, as well as Ambly, the Browser REPL, etc.
What does IFigwheelSupport do?
Perhaps somewhere there is a HUD interface and Figwheel can ask a REPL to display things on its HUD? An iOS or Android-specific REPL could delegate to Objective-C or Java that implement a HUD using platform-specific UI widgets.
Perhaps another thing is the "punch-through" where you add capabilities to talk to the underlying Clojure to do things.
In general though, that's all that is floating around in my mind right now: A way for Figwheel to decorate any REPL with minimal features, based on IJavaScriptEnv, and then additional interfaces that allow them to opt into more extensive features. (Or for other people to independently extends those REPLs with those featueres, given the flexibility of Clojure).
An additional thought: Would
ICompileWatchermatter to Clojure? Perhaps it does for ClojureScript because it must be transpiled? But in Clojure does it only matter when AOT?