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@redrum I actually think it is not needed or logic (assuming all players of a same alliance always winning or losing together) to support talking to single players of a same alliance, but only to alliances, as long as at least one player (meaning the country/power) of such alliance is played by a human player, except that:
if the game has only 2 alliances, then you can talk only to the alliance you belong to;
when you talk with any alliance, the message is always also sent to any human players part of an alliance you have a player assigned to yourself (your teammates always know everything you say).
The above would mean that if only two or less human players are part of the game (either playing a regular 1v1 or with some AI), you have only the option of the general chat (nothing of this feature).
For example, you can have any World War II games, but v3 and Global:
<alliance player="Germans" alliance="Axis"/>
<alliance player="Japanese" alliance="Axis"/>
<alliance player="British" alliance="Allies"/>
<alliance player="Russians" alliance="Allies"/>
<alliance player="Americans" alliance="Allies"/>
In this case, beside the general chat, your only option would be talking with either "Axis" or "Allies", but only the alliance you are currently using a player of, while at least another player of the same is assigned to another human player. This is because I believe in a 1v1 you never reasonably want to talk to the enemy alliance only; so there is no reason to have that option (there is no gameplay related reason to do that).
Of course, if you are playing a 1v1 with two human players, each taking all the players of a same alliance, your only option is the general chat (there is no reason talking to your alliance, since it is only you, and there is no reason talking to the enemy alliance only, because it is a 1v1, as said, thus you are substantially already doing that when using the general chat).
As a pure FFA case, you can have Feudal Japan:
<alliance player="GameSetup" alliance="GameSetup"/>
<alliance player="Otomo" alliance="Otomo"/>
<alliance player="MinorClans" alliance="MinorClans"/>
<alliance player="Miyoshi" alliance="Miyoshi"/>
<alliance player="Ryuzoji" alliance="Ryuzoji"/>
<alliance player="Shimazu" alliance="Shimazu"/>
<alliance player="Chosokabe" alliance="Chosokabe"/>
<alliance player="Mori" alliance="Mori"/>
<alliance player="Urakami" alliance="Urakami"/>
<alliance player="Yamana" alliance="Yamana"/>
<alliance player="Hatakeyama" alliance="Hatakeyama"/>
<alliance player="Asai" alliance="Asai"/>
<alliance player="Asakura" alliance="Asakura"/>
<alliance player="Oda" alliance="Oda"/>
<alliance player="Takeda" alliance="Takeda"/>
<alliance player="Uesugi" alliance="Uesugi"/>
<alliance player="Hojo" alliance="Hojo"/>
<alliance player="Satomi" alliance="Satomi"/>
<alliance player="Date" alliance="Date"/>
In this case, beside the general chat, you could talk with any alliance played by a human player that it is not you (this condition is not actually necessary, as you are never meant to take players across different alliances, but just in case), that is the same as talking to that player, as FFA (if correctly coded) assign 1 player per each alliance (and usually you define both the player and its alliance with the same name).
However, once only 2 human players remain in game (normally, the others have surrendered/raged and have been turned to AI), your only option is the general chat.
As a case of a game with the traditional multi-players alliances, but more than two alliances, you can have Domination:
<alliance player="British" alliance="-Am.P.J.Br"/>
<alliance player="Americans" alliance="-Am.P.J.Br"/>
<alliance player="Japanese" alliance="-Am.P.J.Br"/>
<alliance player="Portugese" alliance="-Am.P.J.Br"/>
<alliance player="French" alliance="-Sp.It.R.Fr"/>
<alliance player="Russians" alliance="-Sp.It.R.Fr"/>
<alliance player="Spanish" alliance="-Sp.It.R.Fr"/>
<alliance player="Italians" alliance="-Sp.It.R.Fr"/>
<alliance player="Germans" alliance="D.A.O.G.C"/>
<alliance player="Austrians" alliance="D.A.O.G.C"/>
<alliance player="Ottomans" alliance="D.A.O.G.C"/>
<alliance player="Dutch" alliance="D.A.O.G.C"/>
<alliance player="Chinese" alliance="D.A.O.G.C"/>
In this case, beside the general chat, your only option would be talking with "-Am.P.J.Br", "-Sp.It.R.Fr" and "D.A.O.G.C", except that if there is no other human player than yourself controlling any players of an alliance you are playing, you don't have the option to talk to that alliance (cause you would be talking with yourself).
So, for example, since "Domination" is usually played with 3 human players, each taking all the players of a same alliance, if I'm currently playing "-Am.P.J.Br", then I will have the three options of the general chat, the "-Sp.It.R.Fr" and the "D.A.O.G.C". If "D.A.O.G.C" is eliminated from the game, and the games turns into a 1v1, because we reload, assigning all "D.A.O.G.C" players to AI (maybe "Does Nothing"), I will have no options at all, since I cannot talk with "D.A.O.G.C", because it has no human players assigned, nor to "-Am.P.J.Br", because it is all me, nor to "-Sp.It.R.Fr", because, since the game is now only between my alliance and that alliance, there are no reasons for secretive talking.
If we would be playing "Domination" with 6 human players, each couple sharing an alliance, then we would have the 4 options of the general chat and all the 3 alliances available (your own alliance would be for secretively talking with your teammate, and the other alliance options would be for secret diplomacy). As said, in this case your teammate should be able to see whatever you say (so, when you select someone else alliance, you are practically selecting both that alliance and your own).
p.s.: In the remote past Wisconsin (or maybe someone else; I'm not sure) actually tried to make a private chat for FFA games, but Sean Bridges (not sure either) refused it; I asked Veqryn about it and he told me that the code was not sound because of some technical reasons, so it was refused, and Veqryn himself wasn't interested in the idea.
p.p.s.: Since automated hosts are moderated (and a mod is judge, jury and executioner), that is to be taken into due consideration, enabling anyone of mediocre intelligence to understand what was going on and make a judgment upon it, or limiting this feature to private hosts only.
