The use case is kind of neat. RAID is great and can mostly solve these problems, but people don't have SATA hardware that can handle the workload well, plus they aren't ready to manage an array like that, and they don't like having to use specific sized drives, etc. Another major issue with those setups is you need to be careful because an IO error that you don't recover from will be very difficult or impossible to recover from because of the layers of LUKS combined with LVM.
With MergerFS you just use regular file systems that are separate, but they get combined into a single mount point. That means each disk can just be a different LUKS encrypted drive and if you need to recover data it's isolated to that one disk and much more manageable. You can also take any disk and plug it into another machine as needed and grow or shrink the storage pool as needed.
MergerFS has options and settings to help you determine how files are spread across the drives, such as least space used or which disk has the most of that directory path already.
My app (Chimera) automates the unlocking of the disks, mounting and some data migration if you want to remove a disk from the pool. I plan to add some rclone features to help provide easier backup options to places like Backblaze, AWS, or a remote server in general.
So far so good and I was surprised at how well Opus had been handling Gtk and pkexec.
Let me know if you guys are interested I am close to pushing some RPMs and DEBs, in addition to the standard Python stuff.