The current plan is to stuff them into a few Gen8 hosts I have. For now, I'm just going to straight-swap 8 of them in for 3TB HDDs in the RAID6 on the Hyper-V 2022 host, and get the system more usable, but I did buy enough to consider building a proxmox cluster with ceph, or similar. So IIRC it's a P420 RAID controller, though I also have a set of low profile 9211-8i controllers literally lying around. Really the only annoyance there would be losing the OS mirror and possibly ending up with 4 hosts in jet-fan mode.
Or I could potentially throw vSphere 8 at it (I have that running on a Gen8 already, so it's possible even if it's not "supported" - for a lab, and with my skill level, vendor support isn't really needed - I do the normal right things like backup and so forth so if I have to restore it's just annoying).
And there are lots left on Ebay, so I could grab another few if I really needed to.