The blog link I offered (above) was from a cofounder of the Lisp Machine company Symbolics.
The problem is that something like GNU/Linux isn't easily hackable. Having the sourcecode under a free license is a precondition for easy hackability, but not sufficient.
The Lisp Machine guy mentioned:
"The XO does everything in Python. You can see all the code, with
a single keystroke (that shows the code of what's running) and
even modify the code."
In contrast, Unix doesn't invite the curious user in. "Compiling" the Linux code is weird -- it's just supposed to be a matter of running a simple program over data, but somehow it's fraught with difficulty and obscure error messages.
(For those who don't know what compiling's all about, it's like when we chew food so our digestive system can better metabolize it. A compiler is just supposed to take a human-readable set of instructions and turn it into a form that a computer can more efficiently execute. Just like you're often not conscious about the chewing process, you usually don't want to be conscious that a compiler is running, either.)
Tayssir