Rack mounting non-rack-mount gear always seemed like an interesting application to me. Raspberry pis, tiny lenovos, network gear, etc.
homelab
Been a few years so I don't have the link, but I bet you can find this (or something similar) online. If all else fails, I hoard all the files I used somewhere on my nas.
Not home lab specific, but a few things around my house to help inspire you.
Cable fingers
Nuc wall mount
Tool peg board mounts
Heavy ass speaker onto a vesa pole mount to get them above my monitors
Couch gaming gear
Sonos wall mount
One of my friends printed this tiny rack for a small switch and two micro PCs. It's pretty cute and nifty
Rack-mounted beer holder.
Jk. But really, anything which helps organize stuff is a worthwhile job for a 3d printer. Even something to loop fibre optic cables on, so that they don't exceed their maximum bend radii, is useful.
I think you'll also find the 3d printer aids in other endeavors. I've used mine to print replacement car trims, ham radio accessories, a photo film spooler, a bushing to convert vacuum hose diameters, and other odds and ends.
This is very multipurpose, but if you haven't heard of gridfinity, there might be modules that would be helpful you home lab, or your home in general.
Here is an alternative Piped link(s):
Piped is a privacy-respecting open-source alternative frontend to YouTube.
I'm open-source; check me out at GitHub.
I have a 10" width rack cabinet where my Proxmox cluster (three mini Lenovo Thinkcentre) lives. I'm currently designing a 10" mount to hold an old phone so that I can see my server monitoring/status through the glass of the door.
3D printing is great for stuff like that.
Special cable trays for your specific setup? Opencompute's rack parts?
Cable management, you don't't want any heavy rackmount stuff 3d printed.
I did a nice fanmount for my Arris NTD, i've also done some toggles to go with paracord to loop up network cabling. Thangs, cults3d and thingiverse are your friends :)
I haven't done it yet, but custom case for repurposed hardware. Mine is a mini PC I acquired free after the m2 drive died. I got an m2 to 6 sata adapter board and it already had an unused SATA port so I'm planning on doing SATA SSD boot with 6x nas drives and print an alternate case for it. Actually powering the drives is the part I'm least sure about.