I played with labeling on a routing matrix before.
Now work on such a thing in Ardour actually started and it’s time to get into details.
These are for the per track or bus connection dialogs; the global routing matrix will be slightly different.
The window title will contain the name of the track or bus, so there’s no need to reiterate it on the port labels. There’s also no need to stick an “out” in front (with the current approach the first label would read “drums/out_1”). With only numbers, labels don’t need to be rotated.
The layout is meant to map signal flow to reading direction. Placing sources on the top allows to list destinations vertically. There are more of them and they can be scanned faster this way.
Routing loops are allowed in Ardour, but to avoid nasty surprises holding a modifier key or having to acknowledge a dialog could be required. Anyway, the cells in question should be marked; in this case with a roughly executed infinity symbol😉
The Show options are radio button trios instead of checkbox duos, because the later would allow to have nothing shown and require more clicking. One could add a list of groups for showing / hiding, but here it’s unfortunate to have split edit and mixer groups.