With today's release of KIO-Snapshot, KDE software now has stable integration of Btrfs file-system snapshots.

For KDE software using KIO, there is now a KIO worker for browsing snapshots of a sub-volume and being able to browse previous versions of a file. There is also a context menu plug-in as part of KIO-Snapshot for exposing different snapshot versions within Dolphin and other KDE software.
1
KDE developer Bharadwaj Raju has been leading the effort around the Btrfs snapshot integration within KDE. A blog post was published today to mark the v1.0 milestone for KIO-Snapshot and showing off its capabilities. KIO-Snapshot interfaces with Btrfs' libbtrfsutil and also integrates with the KDE Frameworks Solid code.

KDE's in-house Linux distribution KDE Linux is planning to soon ship with Snapper and KIO Snapshot for a nice Btrfs experience.

KIO-Snapshot can be downloaded from KDE.org. More details on this KDE + Btrfs integration work via Raju's blog.