I'm hearing a lot of mixed reviews, this is great! It's exactly what I wanted. Pain points are the life-blood of innovation. It's interesting hearing from both sides of the aisle as it were, on what to change or not, and why.
I see the importance, for now, of keeping some backward compatibility. While it's dire that we bring new people into the hobby - as that's how hobbies are kept alive - yet we can't forget those that founded the community. Good point!
A web-based MU isn't out of the question, but to get some players to connect there needs to be a client that, from what I'm hearing, works like SImpleMu (spawns spawns spawns!) but handles TCP and WebSocket connections. I'll have to fire up SimpleMu (I still have it installed) and remember what the interface was like! I'm sure just adding inline spell check would win some people over like myself. Heck, using Electron (which I love) you could have a desktop GUI for that, and a desktop interface for admin tasks as well. With PhoneGap (Cordova) a decent native mobile client isn't out of the question. It would be interesting to apply a little modern UI design to the Mu Window layout/hierarchy/priority and get feedback.
I'd definitely want to use MUX as my jumping point for command structure/style, and update as new play/usage patterns evolve. I like the generalized simple database architecture too. I'm not 100% convinced that the game server itself needs a full-on ORM, or flat-files (JS API's don't care either way).
I'm not sure if I'd make an 'in-game' scripting language off the bat, it's extremely possible to do with JS, but adding commands and systems as Node style Dependency Injection or more so Inversion of Control style container 'plugins' for game developers should be the primary way to add new functionality I think. Something that could be done from the CLI or GUI depending on your style. Want a BBS? drop (or click from a list) a plugin, the MU does a dependency check, and go!
Granted, none of this is 'in a weekend easy mode', but it's all been done before several times that I know of, which could be easy to model from without much more than rote programming to get a proof of concept up. Enough to try and start enticing some open source help.