Thank you for all the great comments and suggestions. I read all of them.
Keeping it simple, the formula for noncombatant empires that I favor is beginning to look like this.
Empire becomes noncombatant 15min after the last avatar in the empire logs off. It is complicated to check all avatars on the same account and a player could easily sidestep this by using multiple accounts.
Units within orbital range of worlds with an empire military base are immune to attack; they will defend that area but they will not pursue enemies outside the area. Thus they become invincible defenders but their range is limited; otherwise someone will put a big invincible station somewhere bad, like near an intergalactic wormhole. The presence of a military base insures that no other empires have cities on the world, to prevent an invincible defense using an alt empire.
All other units continue to attack and defend as normal without immunity.
Harvesters continue to operate. Officers and crew execute their missions. Manufacturing processes grind away.
Keeping it simple, the formula for noncombatant empires that I favor is beginning to look like this.
Empire becomes noncombatant 15min after the last avatar in the empire logs off. It is complicated to check all avatars on the same account and a player could easily sidestep this by using multiple accounts.
Units within orbital range of worlds with an empire military base are immune to attack; they will defend that area but they will not pursue enemies outside the area. Thus they become invincible defenders but their range is limited; otherwise someone will put a big invincible station somewhere bad, like near an intergalactic wormhole. The presence of a military base insures that no other empires have cities on the world, to prevent an invincible defense using an alt empire.
All other units continue to attack and defend as normal without immunity.
Harvesters continue to operate. Officers and crew execute their missions. Manufacturing processes grind away.