My intention is to provide a website for this exact purpose. Multiplayer functionality, the multiplayer server as well as the master server are next on my todo list. (I already started to work on that.

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I can't say for sure when it is going to happen (there is also a slight chance that it isn't going to happen at all. Servercosts, etc...) but if it happens it will be hosted on the current website.
In the meantime players have to host their maps on their own (Dropbox, etc...).
As a workaround (for the time being), I could create a specific forum section where people can create topics for their maps. (Which isn't a bad idea now that i think about it.)