I'm going the route of others with making a fantasy console, and will be content to run it on mobile platforms in an emulator, which is what happens with the pico8.
That said, I do have a half baked idea in my head to make something from a AtMega and an ESP32. If the higher clockspeed of the esp32 is enough to make it pretend to be a valid xram interface for the AtMega. Then output s-video out the DACs.
I am considering teaching a university course where the students implement a NES or GB emulator though. Should be a blast!
I was considering doing the same for my Machine Language class, but it seems that many games rely on the precise timing of the emulation to work. And, because the output was an anolog TV, there are a lot of tricks that need to be figured out. I thought that was a no-go for a course.