With btrfs, you can freely create subvolumes and snapshots anywhere (including nested inside of each other), you can have thousands of them without any noticeable performance impact, and you can easily convert a snapshot to a writable subvolume. I don't have much experience with ZFS, but from reading another post [0], my impression is that this isn't really doable with ZFS. And based off of rift's Readme, I think that these features are required for it to work. But I'm not an expert, so I may be mistaken about something here.

[0]: https://news.ycombinator.com/item?id=45077119