Similar to the Eurorack design there is a backplane that distributes power and potentially some signals. The backplane is finished (see photos). It provides symmetric power (+12V and -12V) plus 5V. There are six slots for modules.

The mechanical design using Lego is also pretty much done. The miniTesla pegboards that hold the electronic components slide between rows of Lego studs and slot into edge connectors at the backplane.

I am currently exploring how to do the front panel. I have found an interesting way to use Lego window frames of size 4x6 or panels of the same size. The window frames are particularly interesting because they accept simple flat pieces of plastic as panes. It is easy to drill the necessary holes into them, 3D print them, laser cut them, etc.