These are a solution to the fully customizable tablet version. If you read the project log about manufacturing I talked about having two different back cover plates essentially. One that is monolithic and neat, only usable for a fixed pre-selected set of peripherals.
The other would be the hacker, maker, researcher option that lets you fully customize position and amount (and kind) of peripherals, making it also easy to add you own custom hardware.

The issue I had to tackle was how do you achieve this without having open sides or requiring 3D printing from the customer.

This is the solution I came up with (pictures below). Each peripheral will have to choose a bezel size. I haven't decided how many I want to include in the mechanical standard yet but it will probably be around 2 size options. They will only be allowed to differ in width, not height. Height is fixed for every element.

To close of the space between peripherals we have spacer blocks, they come in the same widths as the bezels, so if you have give amount of spacer blocks you can always make a closed side surface, even if you add your own peripheral, all it has to do is adhere to this mechanical standard.

The raster length is always a multiple of largest block width. The corners help define this, without them you will run into issues with different screen sizes, so the corners will always extend into each side of the tablet until they form this fixed raster length. That way you can adapt this to any screen size up to a certain minimum size given by the block width.

Finally some pictures of the prototype prints that I made for illustration. This will of course look much much nicer with injection moulded pieces and an aluminium mounting plate instead of clear acrylic :)