I'd pay to get uCity on a GBC only style cartridge. I'm not sure it's existence is super wide spread but this one smart dude figured out how to amazingly convert the original Sim City do the GBC format and even left room for a heap of randomly generated maps and 4 save slots as well. It's quite very well done, has a hint of a few extras the SNES/NES release got the original lacked so it's kind of between both releases. I keep it permanently on my everdrive.
Amazing someone made a manual for it last January and the author was impressed by the work too on reddit where it was posted:
https://drive.google.com/file/d/1...
It got featured over at NintendoLife which you can see here:
https://www.nintendolife.com/news...
Or you could check out this extended play of it on youtube too: