XF 2.0 has been run on a production site for nearly a year, if you count the Demo site.
Is it bad? No, there's definitely no major showstoppers as far as we know. Is it stable? Also no:
https://xenforo.com/community/forums/bug-reports-2-x.91/
Plus there's still a bunch of outstanding reports from the demo.
That said, I'd be more comfortable with someone starting a new forum, at this point, than I would upgrading an existing one. You have no issues with add-ons not being updated, no potential issues with upgrades etc. And, also, the more people that test the software the better and potentially quicker we can be confident that it is stable and we can release the stable version.