I can‘t speak for btrfs, but with zfs you usually are advised to send the snapshots off to another location too. That usecase is highly supported.

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That does definitely replicate the feature of AirDrop more closely. Do you have any experience with it? Does it work reliably?

A thing to look out for is Wifi Aware, which would enable the functionality if implemented. That is what was recently also used by google to enable android<->ios Airdrop