Consider this a warning though: this hobby has caused me to involuntarily collect every model of Z80 powered TRS-80 computer.
If you wish to become hooked anyway, this project might be another good place to start: https://hackaday.io/project/159973-z80-mbc2-a-4-ics-homebrew...
And yep, I now also own many 6502 based computers :-)
Even if you made a version of this board with the footprint changed to the QFP eZ80, it probably wouldn't work because the eZ80 has different memory mapping and clocking differences.
It will probably be a decade or longer until those sources start to dry up, but even at that the Z80 will never become as rare as say, a SID chip.
But this really is a stretch:
The Z80 Membership Card itself is a stand-alone single-board computer that can "power up" your projects, like the Parallax BASIC Stamps or Arduino microcomputers.
Both of those are very commonly called microcontrollers, not microcomputers, since they have all of those extra chips merged into the single package of the CPU.
Take a look at the Arduino Uno [1] which is a very typical (if old) example: you will see that the board is not covered in ICs from edge to edge, since all of the main functionality is in the single-chip microcontroller. I think the second big-ish package visible is for the USB, but that also disappears on more modern controllers with on-board support for USB.
[1]: https://en.wikipedia.org/wiki/Arduino_Uno#/media/File:Arduin...
