When will this capability be available?

Bit disappointing that it's not in. I thought it was supposed to come at the same time as the Steam workshop support ages ago, can't remember where I got that from though. 

Edit: It was mentioned that it would use steam workshop to facilitate multiplayer modding but no timescale was given for it inclusion. Source:https://forums.galciv3.com/465706/page/1/#3552003 about 1 hour 4 mins into the stream.

I don't quite understand why this is such a pain to roll out as it is quite frustrating to have to modify and distribute modded core files in order to play mods in multiplayer only to have star dock overwrite them with steam updates for DLC that you may or may not be interested in. Its just a matter of downloading the files from the host into a temp folder so your game lines up with theirs, its more than likely the workshop side of things that is holding things up and even then its still just a matter of distribution of files.

Until then, I guess its nice enough that modded core files can still be used, its just a huge pain.