Somewhat inspired by Faction Gameplay, I was wondering whether N-Day Factions could be added to NationStates permanently, but without N-Day abilities. Regional officers would continue to be able to create a faction, which would be more like NATO in this case (interregional alliances made voluntarily), and (representative) nations from other regions could "join" the faction (normal nations wouldn't typically join a faction in this case, but could if they wanted to). Factions could have password control, and embassies with the region who established the faction could be upgraded instantaneously to faction status if both sides approved (as they already have embassies with each other), constituting an "upgrade" in status. Faction status could also be downgraded to embassy status instantaneously if one party decides to terminate it. The Faction itself would have regional "Members" listed below its Description similar to how Embassies are listed below regional WFEs.
Similar in style to all NationStates features, it maximizes flexibility and usability, and allows for multilateral interrregional treaties to be symbolized by something above a region rather than a region itself. Additionally, adding such a feature would mostly constitute stripping down N-Day factions and adding password and renamed embassy functions to them, and future N-Day events would just reactivate N-Day functions on existing factions. It's not as bold as most proposals, but it's very realistic and fulfills a need for higher-than-regional level organization.
