Via GC3 itself.  Via New Game, at the Choose Civilization screen, you can select any faction (except those default factions provided by SD), and click "Upload to Workshop". Any new race you of course create will be displayed here as well.   It will even allow you to "re-upload" factions which you have already downloaded from steam workshop, if you decide to tweak them to your liking and share again with the community.  Steam is not checking for content however, as you can upload the same exact existing factions (same name, pictures, everything), which could lead to spamming and confusion. 

Thanks

I had been waiting for 1.1 in the hopes that some of the great-looking content that people are designing in the Star Wars and Star Trek universes may become more convenient to add/remove and show up in collections that bunch ship-packs with faction-packs and unique tech trees. Does anyone have any idea how long it will be until these types of collections will start to appear, or is the combination of these different elements still not possible with the current integration of Steam Workshop?

Thanks for these thoughts dansiegel. I also am really unsure about all this stuff, as I haven't gone into the bowels of anything, but I thought from reading I did elsewhere that the AI basically evaluates ships based on their type (support, capital) and stats, and isn't coded to individually make use of them anyway. Presumably, the design has little impact on its actual use of ships of varying types, even ones you create, simply because it should be making build and use decisions based on the numbers that underlie different designs. 

Also, there must be a way to group ships and factions together. You may be right that there is currently no way to do this, but based on experiences from other strat games on Steam, there is absolutely a way that stardock could have such a functionality implemented in their steam workshop integration. Even without stardock making any further changes, it seems to me that the "collections" feature built into workshop already could fairly seemlessly achieve the desired effect. Again, maybe I am missing the mark on this though. 

I'd love to stand corrected, as that would make sense of exactly why these huge labour-saving and convenience-improvers haven't been made a reality yet. 

Is anyone else having issues with the little buttons for using the workshop in-game?

edit: it might be that I just had to start a new game.  Today I subscribed to a tiny ship and that is available in this new game file, so... hopefully this was the issue. 

Edit 2: minus the workshop button functionality (and lack of Steam Overlay functionality in this game particularly), this seems resolved now.  Just can't use workshop ships in save states prior to 1.1, which I have to concede makes sense.

I've been able to upload my own design (as a test -the design itself is uninspired to say the least), but pressing the "Workshop" button to download other users' ships doesn't produce any results.  It's also worth noting this is the only game (that I've seen) in which I can't even seem to get my Steam Overlay to work, even after screwing around with different global hotkey commands.

I'm thinking either it's bugged because I hit "subscribe" on a couple ships before launching the game, or it's something to do with my PC's displays settings and how this game's engine interacts with them.  Everything else seems like it should've come up in other games at some point...

Elite Founders ship parts probably aren't the cause, since there seem to have been a lot of us.  And I just now tried un-checking "view other style parts" option to see if that had been preventing me from using the workshop to download.

Please, oh please.  I just can't stop drooling at these Federation cruisers.  There's already Akira classes, you guys.