I'm not saying it absolutely prevents people from moving forward. I just fondly remember my first programming environment being an HTML file with a script tag.
It was a real environment, people were doing real things, and I learned based on the (at the time, quite bad) example of professionals. It also made it easy to go on Wikipedia and directly transfer concepts into my program from the pseudocode or C. Learning first in a real language gave me the opportunity to read many real programs very quickly.
I think GoMix and, to a lesser extent, Cloud9 give you a real language environment. I think that's a good step, though I have some minor qualms about the quality of the integrated text editors (which is really the web's fault).
Forget career-ready, I want naturals to never need to be told or convinced to program.