Just found out that Bryan Shannon who worked at Maxis/EA on Sim City (and was laid off recently) started a Patreon campaign to be able to work on modding for Cities: Skylines. Pretty cool if you ask me because the guy seems to be pretty talented. 
https://www.patreon.com/gula
He also shared a vid of his creation process: https://www.youtube.com/watch?v=haio5OWhYD8
https://www.patreon.com/gula
He also shared a vid of his creation process: https://www.youtube.com/watch?v=haio5OWhYD8