A nice idea, executed by Malik Enes Şafak, to use an 8x8 RGB button matrix as a front panel, in this case for 6502:
Here, it’s a repurposed ‘Launchpad’ grid-style music controller, which has 64 RGB buttons and 16 other buttons. It just might be that one could rig something up using four 4x4 kits. Or maybe there are other affordable ways - indeed, this idea could be implemented on a touchscreen or using a browser.
The 6502 is a good match here, maybe with A, X, Y, SP, PC and the status byte taking up 7 of 8 rows. Perhaps the 8th row could be a representation of the IR or the databus. The Z80 has far too much state for an 8x8 front panel!
Hat-tip to @DavidG