Proposal for Capital City Variant:
1) Players declare at the start of the game which home SC is their capital city. This cannot be changed throughout the game. Lose that capital and you cannot build.
2) Lose the other home SCs as well (all of them to one power) and you become the vassal state of the power controlling your country (defined as the power occupying your capital and all other home SCs). You are completely under his/her control regarding the deployment and use of units. You could be allowed to gain SCs outside of your own borders but only with their consent. And, whilst a vassal, you cannot build regardless of external gains.
3) Your vassal status will change if your capital city and all other home SCs are taken by a single different player - you then become his or her vassal...
A miserable existence if you are caught out in this way but a fascinating use of power for those who gain an early ascendency. It also places a premium on holding onto the designated Capital as well as allowing for some thought about which SC to designate in the first place.
However, there is some hope...
4) As you become a vassal by having all of your SCs under the control of one power. If that power, at some stage later, loses any one of your SCs, you are released from vassal status. In this way, an ally can rescue you. However, the continued loss of the capital prevents you from building units.
5) Whilst a vassal, you can communicate with other players but must move units according to the controlling power's instructions.
In this way, although you can be forced to provide the armies and navies for warfare, you retain the ability to leak plans and generally work behind your master's back... Something which should feed the revenge motive for those unlucky enough to be conquered at home.
I would like to try this variant and am looking for players. If you declared an interest when I first flew this idea (before Christmas) please let me know if you are still interested.
And, of course, the game would follow an honour system: joining players must agree to abide by the specific rules.