So, there's a whole host of issues with the frame - aka the core of the whole project - that were becoming a hinderance to further upgrades and new modules.

1. Removing most components meant first removing the keyboard. This is a huge hit to the modularity aspect. I'm fixing that by, at this stage, making a separate slide-out tray that the keyboard sits in. Haven't decided on the mechanism to lock it in place yet, thinking either magnets or some sort of compliant mechanism spring catch. The added benefit of this is that other keyboards (at least ones the same width or less) can have a tray made for them and slot into the same frame. I'm also going to remove the slot at the back for the keyboard USB C cable and make it internal, that way the keyboard slides onto the USB C connector.
2. The rails had three different spacing increments. This was done to facilitate precise positioning of modules instead of moving the rail slots on the modules themselves, which is what I'm doing now. The rails are now evenly spaced apart pairs.
3. Even with the inclusion of the USB hub, it still had wires poking out the back. As mentioned in an earlier log, pogo pin connectors are the plan to fix that. They've arrived, and I had to remake the whole backside of the frame to accommodate them neatly.

I've gotten a more compact USB hub, which is actually taken out of its original casing to reduce unnecessary size. The underside compartments will be a lot slimmer than the previous ones.

I went ahead and placed an order for a HDMI magnetic connector. When that arrives, I'll decide on a position on the back of the frame to affix it.