Allied Victory Rework

Allied victory has been broken for a long while and is due for a serious rework or even removal due to the amount of possible abuse it opens up in both single- and multiplayer. The salient issue is the instant change of victory thresholds when a member enters or leaves an alliance. This opens up ways for two opposing types of abuse

• Powerful players who have never cooperated in the game can instantly reach victory in one turn if they notice they both have the required amount of systems, capitals, generated Dust, victory techs or victory wonders. There exists no counter for this strategy, it doesn't really encourage long-term cooperation and it encourages only the strongest players to ally together.

• On the other end players already in a more long-term alliance can abuse the fact that other players or more importantly the AI have no known way to track the individual members' personal victory progression, because the alliance is counted as one entity for the purpose of victory. This means a player can join a big alliance for protection, reach some victory type on their own while inside the alliance in almost complete safety then leave the alliance and win in one turn when their victory thresholds return to normal.

The purpose of the reworked alliance victory is to

1. Faciliate long-term cooperation between all parties in an alliance attempting victory
2. Give other empires outside the alliance a chance to react and counter allied victory
3. Prevent the abuse of one member coat-tailing in a big safe alliance then leaving to reduce their own victory condition thresholds

The way I see it, there's several mutually exclusive ways these goals can be achieved:

Permanent Alliance + Old Victory Conditions

Alliances attempting a victory together are locked in place for the remainder of the game: maybe a late-game tech or some other unlock that gives the ability to do it, and also requires X number of turns in normal alliance before being able to commit to it. The process itself should take some turns as well before applying, and when doing this other empires are warned. 

Why this would achieve the above three goals:

1. Staying in alliance for a long time is base requirement for initiating permanent alliance and allied victory.
2. Announcement of the creation of a permanent alliance and grace period before new victory condition thresholds are applied to the newfound permanent alliance gives other factions a chance to react.
3. Permanent alliance attempting a victory together can't be broken, so players can't coat-tail behind a larger alliance and leave it to instantly reduce their own victory thresholds.

Idea is you would separate normal alliances and permanent alliances. Former are merely temporary, prone to being broken and don't count for the purpose of victory, while the latter is the only form of allied victory. The AI should also be aware of the difference between the two, especially if its friends are close to winning and make a demand accordingly: "either create a permanent alliance with me or we'll break this normal alliance".

Reworked Allied Victory

Remove other victory conditions from Allied Victory and rework the latter from scratch. 

Allied Victory is its own victory condition that has nothing to do with normal victory conditions, and normal victory conditions' thresholds are completely unaffected by the alliance. Possibly something similar like above idea with an allied victory you have to initiate and announce beforehand. Since this is a big deal, there could be a vote between alliance members.

SMAC for example has Diplomatic Victory, where after initiating it you have to defeat the remaining enemy factions before being able to assert hegemony. Alternatively if that's too warlike, make Allied victory something defensive like the alliance attempting to hold their ground while producing something (Influence anyone?), or control certain areas, anyways there's plenty of possible options for a completely reworked Allied Victory. 

It's very important that the stuff controlled or produced so far doesn't directly help the allied victory, f.ex. old Economic+Allied victory where all Dust produced by all members so far in the game are directly applied, resulting in a victory in one turn. If the new allied victory has the members produce or spend something instead of fighting, it should be something that starts counting from the moment the alliance victory attempt is started.

Like the above idea this would achieve the core goals:

1. Whether it's destroying all opposition or spending Influence, or something else entirely, it gives all members a new objective they have to strive towards together.
2. Since allied victory has nothing to do with normal victory conditions (other than existing infrastructure and military helping you achieve the new objective quicker), powerful, previously completely unrelated factions can't win instantly in one turn by announcing a new alliance.
3. Since allied victory and normal victory conditions are unrelated, there's no threshold abuse.

However for the third point to work there also needs to be changes to victory condition tracking. Members in an alliance in particular need to be able to somehow track each other's victory progress so they can null the alliance if fear one of their members is close to approaching their personal victory. This obviously calls for changes to AI as well, so it knows when it's in an alliance where it's going to lose due to other member achieving victory first.

Remove Allied Victory

Exactly as it says on the tin, cutting the knot. Like some other 4X such as Civilization V, all alliances are merely temporary and there can be only one winner. Gets rid of allied victory abuse altogether, and maybe makes late-game more competitive as factions change between trying to win on their own while allying together for military and economic aid to prevent a stronger foe from winning. 

The first goal is skipped, but the second and third achieved for obvious reasons. Fixes multiplayer instantly, however like the previous idea, in case of single player the AI needs to be able to realize when it's in a non-beneficial alliance where one of the other members is about to win, so the player can't abuse friendly AIs.