Yes, actually I've looked over all the shells on that wiki page. I think most of them haven't taken off because they either their host language has been poor or unpopular, their design or implementation wasn't great, or they haven't really solved the right problem. I think the idea of embedding a shell into a general-purpose language still has a lot of merit. Most of those projects trying to embed a shell DSL into a general-purpose language, scsh included, are basically for programming and not interactive use. Shells that are only interactive or only for programming end up fulfilling less than half of the purpose of shell, in my view, because the interaction and scripting feed back into each other in a virtuous cycle. The only ones on that list aside from Rash that try to be embedded in a general-purpose language while being good at both interactions and programming are Xonsh and eshell. Xonsh is pretty new (I wasn't aware of it until after I had made Rash), and eshell is in Emacs Lisp (which is not a very good programming language or platform to build on for anything except extending the emacs editor).
Rash also tries to be better than the competition by adding object pipelines (much like Powershell, it makes it much more reasonable to make system administration commands in the host language, and have rich interaction and inspection of command results), user-defineable pipeline operators, and generally tighter integration with the host language while still having a light syntax for basic commands.
I would like to be able to have my command language tightly integrated with my programming language, and be able to define my system administration commands (and interactive shell plugins and completion) as functions in the host language (while still being able to naturally use external programs). And I would like my shell scripts to be able to grow and potentially even turn into full-fledged programs, or modules of some larger program. I think there are a lot of benefits to the approach I'm using (which would be too long for a comment here).
That said, I'm not holding my breath for it to catch on widely any more than I'm holding my breath for Racket to take off as a popular programming language (although I frankly wouldn't mind either one). I think a better Posix shell is certainly a noble effort, because whatever better shell does become popular, we certainly need one. And an automatic upgrade path for existing scripts sounds great. So I salute you and wish you good luck with it. Also, as someone looking at shells and their features to copy the best ones, your wiki is a great resource. So thanks.