Utilities like Anaconda, GNOME Disk Utility, KDE Partition Manager, and Gparted, ideally should be able to support Btrfs shrink.

Related issues being tracked

btrfs-progs: bogus min size estimates by 'btrfs inspect min'

libblockdev: btrfs plugin missing a check for minimum file system size for shrink

udisks: btrfs resize improvement for multiple devices

gparted: btrfs: shrink underestimates minimum shrink size

anaconda: add support for resize of btrfs filesystems

Shrinking a single device btrfs is easy, the kernel does most all the work. Multiple device shrink is harder, which devices to shrink? What does the UI look like? It might be true some utilities will opt out of shrinking multiple device Btrfs.

Another issue is whether anything can be done about the kernel's obstinance, refusing to update the in-memory partition map, when the disk is in-use. Thus required a reboot, unlike dm/lvm partitions.