The idea was to have a 6502 'super system' that would fit in a shirt pocket. Because I firmly believe that enhances my geek-factor. Besides, it would enable 6502 fun, any time, any place.
The esp32 builds on my KIM Uno project of some years ago. That is a pocket-sized KIM-1, with exactly the capabilities of the real machine (although with lots of software built-in). It neatly filled up an atMega328 microcontroller's available RAM, CPU capabilities and I/O pins.
Now we live in even more modern times with things like the esp32. All of a sudden there is loads of RAM, Flash storage and wireless connectivity to play with. In fact, so much capacity that it is hard to fill it all up with retro 6502 goodness.
So I tried to make the esp65 into a lot of things at the same time. That can be criticised as lack of focus. But this hardware set will open up lots of retro projects I can waste my time on. It can be a Z-80 CP/M system, a VT-100 terminal for my PiDP-11, a programmable 6502 calculator, anything really. Hence, the mix&match 'modular' approach. Of course, I hope others will find it fun enough to add their ideas to it.
The other design goal: make it as low-cost as it can be. Standard parts only, and nothing more than the esp32, switches, a display and a cheap, standard case. This is a toy, and high parts cost only diminishes its fun factor. That also means I accept shortcomings. For instance, the hinge of the case is simply screwed on and needs to be propped up with a pen or something to stand upright. Otherwise, it will just open up the full 180 degrees.
And the wiring between the two halves (keypad and display) is simple wires, not a fancy flat-cable that needs expensive connectors. The goal was to make it robust and sturdy (so I can really carry it around), but cheap enough to make many of them (so it's not a disaster if it gets lost).