No it's not. Technically speaking yes, but without Python there would be no RPython. In other words you're betting on three language/vm communities: Ruby language, Python (RPython!), LLVM (iirc).
I don't believe introducing a lot more dependencies and complexities will cure any problem. Sure, it's a nice project and the work shows the great skills of the developer. But it's not practical to use this besides some non-crictical fun projects.
Yes, but betting on Python is the whole point of PyPy. The idea is to build a toolchain using a relatively high-level programming language like RPython to build new languages.
As far as I understood is that this allows for low-level concepts to be changed more easily, while low-level implementations always suffer from basic decisions (e.g. you will never get reference-counting out of CPython, while you might be free in to change that in an RPython-implemented language).
So, the entire point of PyPy is being able to implement other high-level languages in RPython, so an attempt to implement Ruby is definitely very interesting! Also, the resulting binary is not depending on Python whatsoever.
That's not really rebutting the GP's point, though, which is that despite using a Python-derived language, we're not running Topaz on top of a Python runtime.
I don't believe introducing a lot more dependencies and complexities will cure any problem. Sure, it's a nice project and the work shows the great skills of the developer. But it's not practical to use this besides some non-crictical fun projects.