Could you explain more what's wrong with the STM32 family as a target? The Playdate's got a complete implementation and an STM32 heart. And other members of the family have seen other non-system-specific implementations, although neither is complete. I'm not deeply familiar with the family, so insight is welcomed, but I don't immediately see why they'd be unsuitable.
And while they're far more numerous, ultimately I think they're less likely to be used for personal computing. Sifting through the ruins, if you can find any functioning personal computer, you can get started immediately. Even if you don't have a compiler, you certainly have a web browser and write permissions. All you need to bring is the emulator spec.
That's an easier bar to clear than harvesting chips, a set of other working parts, gathering documentation for each, ensuring you have tooling and likely libraries for each, and most critically: enough existing, functioning tech to program it all. But if you already have that, you already have everything you need to compute without bootstrapping a new device. Not to say it wouldn't be worth the effort, but it's not an easier or alternative path to personal computing, just a path to share or persist it.