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!
I’ve looked at the 4x4 kits you mentioned, and maybe they can be found cheaper elsewhere, because when all is said and done you might be better off buying a used launchpad which can be had for as little as $40 US if you go hunting. The Sparkfun BOM looked like it was pushing $60 USD.
Or just use a stateful front panel? One 4×4 split in half to give 2×8 makes a nice set of switches/annunciators for 8 bits, and then a few buttons at the side could let you switch these between address bus high/low and data bus. Or just go all out with three of them (plus the additional side buttons/switches) to give a full standard 16-bits of address and 8-bits of data switching/annunciation all at once.
(I’m thinking more of a standard front panel interface to a real machine here, rather than a simulator panel; given that your simulator is almost invariably running on a machine with a decent display, adding an extra external device to give annunciation seems like a bit of a toy to me. But then again, I suppose what we’re doing is all toys…)
If they were really toys,scale up to make a 8 x 8 lighted floor,
with sense switches. To boot you just hop from spot to spot.
Or make a nice lighed dance floor, or demo program display
The real computer is the Datatron 205 in the rusting loft.
