The d-sub connectors I've been planning to use in this project came in the mail today. They'll be used to send power and data to each removable tray holding a raspberry pi. You may recognize it as a vga connector - it's a very common part picked specifically for an easy to reproduce build.
I also did a quick test print to check if my mounting points were accurate. The print looks minimal but it's actually a part of the larger rack model that has been chopped out.
Even with the plastic mounted, the connectors are a bit difficult to separate. Hopefully these connectors will loosen up - I recall VGA cables being generally pretty easy to disconnect. I'm planning to add a locking mechanism to keep each pi tray snugly in place, perhaps the same mechanism can pry the tray out if operated differently. I haven't designed a locking mechanism before, so it will be a fun experiment. Regardless, the mounts pictured above were a success - with M3 screws (socket-cap ftw!), the clearance is perfect.