I wired some of the diodes, for the digits 0 to 5, and there are "ghost segments".

My plan of using a bidirectional diode array has failed and the prospect of using much more relays looks bad...

The 4-bits decoder with 10 relays works great, as shown in the video, but things get dirty with the diode array. The germanium diodes drop about 0.6V, and ghost segments come from loops with other codes. This feeds the filament with another voltage, 0.6V less, not much but enough to be seen.

One solution is to add diodes in series to increase the drop so the ghosts are much less visible. This doubles the quantity of diodes... Or use Silicon diodes, with little benefit. This increases the power supply voltage... for nothing.

The other solution is to go "full relays" and that means 15+3=18 relays, double the planned quantity, much more space is used, much more power is used and it's much more expensive! A 4-digits display will use 72 relays !

Another is to use octal only. That's 9 relays and a 16-bits display uses 5 modules and 9×5 +1=46 relays. But this is not coherent with the front panel  dials (in hexadecimal).

Yet another possibility is to keep the same 10-relays circuit but replace the LEDs with diode+Glühbirnchen, and one Glühbirnchen per digit is used... This gets us rid of the diode arrays and 7 segments tubes but would lose a lot of the appeal.

Hexadecimal is hard !