Would you mind saying why? It isn't unstable or anything, just unfamiliar, in that you can't write C programs on it. But people do use it in production.
Well, it's always safer to use widely used solutions in production. That way you encounter fewer bugs, and it's much easier to find a workaround in case you do encounter one.
It's slow and doesn't run any software people usually want to run in production. If your "production" needs are something Plan 9 is actually tailored to, sure, go ahead.
I run it as my primary development environment, but what I do is pretty specific, 99.9% people need something else out of their development systems.