But I have to second cjsuk, User RPL and System RPL are not programming languages you'd want to use nowadays for larger projects. Personally, I'd like to see Lisp on such a device, but any kind of Basic, Pascal or Lua like language with built-in hashtables and structures should be fine.
Anyway, as it looks now, the HP50g will be the last calculator I own. The companies apparently think that the market isn't big enough. I believe there is a demand for a machine like the above one, especially if it's also water proof, but maybe I'm wrong.