- closed information - Each player holds cards in their hands that are hidden to other players. Additionally, Action Card selection is hidden until all actions are revealed simultaneously.
- not a trick-taking game - Unless I drastically change the rules, this is most definitely not a trick-taking game.
Obviously the first point (partnerships) is the easiest to implement. For my design process, I focused on a four-player game, with two teams of two players each.
The only point that remains is to allow the players to communicate through play. Obviously there are a lot of other logistics involving how to players can play as a team, but I felt it was more important to focus on communication and let the details grow from that.
As noted above, there are primarily two aspects of the game that are hidden: cards in hand and the action selected by each player. These are what partners may wish to communicate to each other is some form.
When you consider a trick-taking game, usually the communication is open so that all players have a general idea what is being communicated. Leaving Bridge out of the discussion (as I am not qualified to speak to it), in many trick-taking games, players will play cards that do not affect the current trick to signal something about their hand. In RftG, if you are playing something that is ineffective, you are playing inefficiently and are going to lose. Therefore, another form of communication is necessary that does not require for inefficient actions.
I believe the best way to communicate with another player in RftG (without table talk) is to pass action cards and/or hand cards.
Action cards would be the easiest, as partners could share their planned action first, and then have the option for one or both of them to switch actions before playing them. This would require some verbal communication ("I'll switch mine. You keep yours."), but it would be a simple way for two players to act as a team. However, I think the uncertainty of non-verbal communication leads to more rewarding play. There are also other balance problems that would have to be worked with (Produce-Consume strategies would be especially strong).
Hand cards provide a variety of methods of communicating. Players could exchange cards, show their partners their discards (and perhaps allow them to exchange a discard for a hand card), or players could even openly discard as a way to openly cue their partner.
Unfortunately, the ways to communicate hidden information is not the most problematic portion of creating a partnership game out of RftG. Larger issues of balance with two players working together would need to be worked out. If I were pursuing this more seriously, I would consider setting up the game like a 2-player game with 2 actions per turn, and each partner is selecting an action. A shared tableau between partners is a possibility, but only if a system can be devised to determine who gets cards from trades and consumes (perhaps the one who chooses the phase IV action?). There are several routes that this could take, but lots of playtesting would be needed to determine if the game ultimately breaks when two players are able to share information.