Add the game to steam
Why I think it will be beneficial:
* it is very popular and it's website has a lot of visitors (Alexa ranks it as the 314 most popular website on the internet).
* Seeing a lot of good reviews can really tip the scales and make me (and probably others) take a chance on trying a game (it's basically social proof), it could lead to more exposure which will mean more developers and more feedback (former developer of naev said it brought new developers).
* Steam is the only game review system that i know of which is able to rank games only based on "recent reviews", so if a game starts badly and keeps getting developed and becomes good the old review don't prevent it from getting a good rating, this is especially good for open source games that can have a very long history of development (being developed for more then a 15 years is common).
* Another nice feature of steam is that you can find reviews for players that played more then a certain number of hours , some games can be half done and a review after three hours of play time might not reflect problems, a review after say 30h indicates you can pour some time into it without the game failing (and you will have to wait for a newer version and maybe play it until the point you reached before because save files are not always compatible with future versions).
* Some FOSS projects on steam have a price (for example the game Mindustry ). Maybe you could use that for funding and paying freelancers to create graphics and sound (iirc this is what shattered pixel dungeon does).
* early feedback can be useful, there is a saying that if you are not embarrassed when releasing the software then you released it too late, steam can mark a game as early access (like supertux does) so there is no danger of disappointing players because the game isn't fully polished.
While I agree releasing on Steam for greater visibility is a nice idea, the one concern is that Freeciv is a game you need a keyboard to really play (at least as far as version 2.6 goes) with its current user interface. Without a major UI overhaul, I think the game would get too many negative reviews since graphics and controls are a major detractor for many games on the platform. Not to mention, I can't ever see myself playing Freeciv on mobile or a standard tablet (especially when the game is crowded with dozens or hundreds of units on the board in larger gamaes).
But if someone could make a mobile edition of the game (with simplified controls), that could be released on steam. Personally, I think making a demo version (allowing small games, ie: up to 10k tiles and up to 5-6 players) and allowing folks to download the full game for either mac or pc would be the better direction since the base game is free to download anyway
Why do you think using a keyboard is a problem? I think most of the games on steam don't need a keyboard.
Regarding the graphics, there are open source games on steam with graphics that are less impressive and seems similar to freeciv, but are getting very good reviews (better then commercial titles that probably cost millions and have shinny graphics), examples include supertux, battle for wesnoth, endless sky and Mindustry.