I'm working on a project which I have explained on the following link: http://xlnation.net/content/mercurial-s ... r-citiesxl
It is still in testing, but the general idea is that you use the Mercurial software found here: http://mercurial.selenic.com/
With the proper instructions, you download the game save files *and* the patches from here: http://hg.mik-maq.com/citiesxl/
I still have to sort some problems out with it, then I need to make tutorials that guide people how to FIRST save their existing stuff THEN fetch the public version. If they wish to have write permission back into the repository, then there is yet another tutorial that would allow them to get write permission back into the project.
Once it is working, I'll try to remember to post back here for anyone interested in participating. It just takes extra effort because, as User said, you have patch files in one location and the game save is in yet another location AND you have to have the same game version AND anything like the current version of the User Interface Mod from XLNation loaded in. If you don't have the same stuff, this project will not help you.
But it would be a way for you to 'see' the cities that I create, and if you wish to participate, you will be able to 'share' your city with others.