Actually I tried to do this a few years ago, but with some kernel hardware support issue I have to give up, now as my Linksys WRT1900AC v2 is retired from network, I decided to have another attempt, with some success.
Here is Linksys WRT1900AC v2, with ARM Debian Buster installed. The router has 1 x USB3 + 1 x USB2 (combo port shared with eSATA 6Gbps), I used USB3 to host root FS, leaving the valuable eSATA port to connect a 4-bay 3.5" eSATA enclosure. The enclosure has no RAID function, the router eSATA were known to support port multiplier, a couple years ago my failure was due to old kernel doesn't support SATA PMP, and only 1st drive can be recognized (Well you can still use it as a 1-bay NAS, but I don't like it).
Manual OMV 5.6 installation, it has quite a lot of custom things to be done. For example my kernel has no quota/BTRFS (after compiling kernel module still doesn't work, so I give up), ZFS not supporting 32bit ARM so I know there is no hope. All these requiring extra configuration and setup. The 1st picture was showing I have a 8GB USB flash memory as root FS, but later I changed it back to a normal 2.5" USB HDD because I don't want it to be killed by kernel compilation + OMV logging that soon.
Hardware supports HDD hotplug, OMV has no hassle with this, every single plug/remove event just need a simple scan (sometimes I don't even need to).
eSATA has much higher stability, I inserted 3 x 4TB 7200rpm drive to build a RAID 5 volume, hdparm cached disk read gave me a 320MB/s transfer rate, and CPU loading/memory usage still low.
The next thing I am still working hard on is the LUKS disk encryption, (my CPU has crypto acceleration) it says failed to create, but no actual errors, I don't even know how it was dead 
Wanted to use docker but kernel has no virtual ethernet support (veth), I compiled but after pulling container the system went crazy, I guess docker on 32bit ARM isn't very usable? I am still wondering what else I could do because almost all plugins moved to dockers.
