I'm running btrfs in production with a very heavy workload with millions of files and all sorts of different access patterns. Regular deduplication runs, too. We're probably one of the largest btrfs users.
Had a LOT of unplanned downtime due to various issues with older kernel versions, but 4.10+ has been solid so far. You definitely need operational tooling (monitoring, maintenance like balance) and a good understanding of the internals (what happens when you run our of metadata space etc.).
Happy to answer questions!
On a related note: Never ever use the ext4 to btrfs conversion tool! It's horribly broken and causes issues weeks later.