Masaki Crafts successfully transformed a broken 1984 Sony Watchman into a functional Game Boy Color. The modified device features a cartridge slot, HDMI TV output, headphone jack, and a link cable port, along with an SNES controller port for HDMI use.
It is definitely rough. But given these things were from the age of analog television, and therefore would fail to receive and show digital, HD, content, I applaud the reuse of what would otherwise be a paperweight/landfill fodder.