I imagine you'd see a return to the TTL-based computers of the 1960s and 1970s.

If you still have access to modern manufacturing at the PCB and simple component level, something in the veinf of retro-hobby projects like the [MOnSter 6502](https://monster6502.com/) and the [Gigatron](https://gigatron.io/), which reimplement a CPU using only TTL logic chips.

(ie. chip designs from before [VLSI](https://en.wikipedia.org/wiki/Very_Large_Scale_Integration) that are just the 1960s-state-of-the-art way to pack 3 or 4 transistors into a smaller, easier-to-wire package.)

The Gigatron kit does use a RAM chip and a ROM chip, but those can be built using transistors and diodes. They're just significantly more bulky and, since it's a hobby kit focused on making a CPU without a microprocessor, it'd be counter-productive for the Gigatron to do that.

(See [Visualizing ROMs 1: Diode Matrix ROM](https://www.wintergroundfairlands.com/2013/10/visualizing-roms-1-diode-matrix-rom.html) ([Hackaday](https://hackaday.com/2013/10/18/making-a-diode-matrix-rom/)) for more on building ROM from scratch.)