Sorry, only just seen this comment. Just in case you're still following this thread and interested in a reply:

I'm aware of Elvish and really impressed with what's been built and the traction that has gained. There is definitely some overlap between murex and elvish but also a lot of area's where our shells differ.

I think there is sufficient difference between the two shells to justify their existence.

Oh, definitely. Just thought it was something you should check out and I didn't see it mentioned anywhere.