Not sure what the multidisk consensus is for btrfs now-a-days but adding/removing devices is trivial, you can do "offline" dedupe, and you can rebalance data if you change the disk config.

As an added bonus it's also in-tree so you don't have to worry about kernel updates breaking things

I think you can also potentially do btrfs+LVM and let LVM manage multi device. Not sure what performance looks like there, though