Little things such as the auto-indentation requiring the use of semicolons and locked to 4-space, lack of highlighting for client supported es2017 features (e.g., class, async/await) and no dark theme is indeed annoying; however, larger issues such as network syncing being delayed or disconnected can be incredibly disruptive. I wrote a simple auto-learn class earlier and found out that a timeout disconnection had occurred, and after logging back in and going back to my scripts they were entirely gone. I imagine they didn't get saved correctly and a reconnect refreshed from the server.
One solution to these problems would be an API to upload scripts from my local machine to the hosting server via network call as well as downloading existing scripts. A simple oAuth protocol would be enough to stop most attempts at tampering with server code from unauthorized users and could use the same authentication as the game since scripts seem to be per-character anyways.
A syncing service would be a significant improvement over even Mudlet, which always annoyed me enough to make me write a complicated script to load files from my machine instead of using their built-in editor. It may also encourage more developers to start writing systems using Nexus, which in turn helps support new users by providing easy to find utilities for the client found on the website.
I'm assuming that the game admins and developers read these forums, and I would love some feedback. If there is a better way to submit this suggestion, I'd also want to hear that.
Edit: As an aside, this could be a gateway to a hosted script marketplace, downloading packages directly to user's accounts via a simple click.