[Dagger2]

You don't need to stack ZFS-on-LUKS-on-ZFS, you just need to put ZFS onto LUKS rather than onto the raw disks.

The downside is that you have a choice between encrypting all file data twice, or losing the benefits of ZFS's encryption (mainly the ability to send snapshots to another pool without decrypting them). It would be nice if you could specify a pool key to be used to encrypt all blocks not covered by ZFS native encryption, which would eliminate the need for LUKS.

[pstch]

Yes, and there's another downside to that : it makes me lose the other ZFS benefits (raidz, mirroring, some level of performance).

[Dagger2]

Use one LUKS volume per raw disk. You'll still get raidz/mirroring.