"The world already has enough von-Neumann-style languages and people working on them"
I believe mahmud was being ironic.
Slava's very smart, but I think that the basic idea of a 'stack based language' is simply not a great one, because keeping track of the stack in your head is a pain in the ass. So I'd say that mahmud is right on. Worth learning for fun, but it just doesn't strike me as practical.
Good Factor is more about combinators than stack juggling.