I'll have to give yours a spin too. I'm glad there's a lot of shell innovation right now. I'm all for breaking posix shell standards and creating things that are way more usable. Fish's prompt customization, functions, highlighting, completion and searching are pretty amazing.
I realize a lot of these little projects will come and go. No matter what, they're great learning tools for the creators/developers, exploring what it takes to make an interactive shell.
Still, I hope we see more stuff like fish come out (and make no mistake, fish took a lot of years and a lot of devs. In the early days my instance would crash every once in a while in ways I couldn't easily reproduce). It's great that we're finally getting away from the traditional bash/zsh/ksh stuff and into newer shells that make coding and navigation easier.
The goals of mine are akin to Fish in terms of REPL use but with a greater emphasis on scripting.
Like Fish, murex also does man page parsing (in fact I wrote mine before realising Fish did the same), but unlike fish autocompletions can be defined by a flat JSON file (much like Terraform) as well as dynamically with code.
Currently I'm working on murexes event system so you can have the shell trigger code upon events like file system changes.
My ultimate aim is to make murex a goto tool systems administration tool - if just for myself - but the project is still young
[1] https://github.com/lmorg/murex