Also SimCopter had an easter egg in it that a programmer inserted without permission where on his birthday and on his boyfriend's birthday, the city would be full of men in swim trunks holding hands and making kissing noises. I remember there was a controversy about it at the time, they fired the programmer and released a patch you could download to get rid of it (which was pretty unusual at the time) :(
https://lgbtqgamearchive.com/2015/08/31/gay-sims-easter-egg-and-controversy-in-simcopter/
Anyway, if the Cities: Skylines people ever did something like let you play entirely different games on a map of your city... I would give them all my money