Same here. Had a production node running btrfs under heavy write load (lots of small files, frequent creates) and spent two days debugging what turned out to be filesystem-level corruption. Switched to ext4 and never looked back. The article doesn't mention what filesystem sits under Versitygw here, which seems like a pretty relevant omission for anyone thinking of replicating the setup.
I'd worry about file create, write, then fsync performance with btrfs, but not about reliability or data-loss.
But a quick grep across versitygw tells me they don't use Sync()/fsync, so not a problem... Any data loss occurring from that is obviously not btrfs fault.