I think I was thinking about how I would work a MMOSG. I'm not sure the game community is ready for MMOSGs, or ever will be, but I think it would be neat-o.
Anyways, the idea is to make the galaxy big. Big enough that you can't blow it off in a solid 12 hour day of power gaming. Now that you have a really big, persistent
galaxy, you start your fledgling space empire. You have just developed ftl travel. Commence the explore. Look for colony worlds. Watch out for hostile aliens (which may or may not be other players).
The turns should take at least a day to process. That is the system should be capable of handling the maths in short order, but you should then have a day to respond to the changes. Shorter if you're slightly off-center and your work doesn't care about you logging in from your workstation during work. Longer if you need more time to schedule conflicts (and plan). Conflicts should be scheduled as much as possible between players. Conflicts with simulated opponents can be resolved at your convenience. Now that's not all that realistic, but is a concession to the fact that the
average player of these games is often better at tactical combat than the
average simulated opponent (SO for short).
The combat module needs to have layers (like an onion). On the top is the strategic layer. You can have input on this from three perspectives. One is as an aggressive combatant. Two is as a defensive combatant. Three is as an observer. In case one and two you probably want a facility to have doctrine in place ( a common set of rules for encounters) to help you quickly set out your game plan for the engagement.
This will most likely be related to your objective in the engagement. The battle planning sub-module needs to encompass all of the possibilities of the battle simulation. Each side needs to commit it's forces to a plan before proceeding to combat (battle simulation).
Battle simulation should take place in the largest definable useful area, which I figure is a star system. The combat in space around the bodies of the system should take place while the combat on the bodies is occurring. So the ground invasions are occurring while you're fighting in space. Morale needs to be a factor for a "truer" simulation. Not everyone will fight to the death if they are given a more attractive option.
You should simulate the model in 3 dimensions using "pseudo" Newtonian physics in "real time". With the acknowledgement that these things need to scale into a "playable" time frame. Using the Solar system as an example, we probably need to
scale the time frame up relative to the speed and range of weapons. We are dealing with a truly tremendous volume of space. The amount of scaling needs to relate to the achievable speed of the ships involved and the range at which weapons become effective, and perhaps more importantly, the sensors become effective.
I'm neutral on your level of input on what happens on the ground. Certainly, if the pace is slow enough, you could have a secondary UI which allows zone by zone control of invasions, or bombing. I do think that the minimum will be the ability to organize your ground forces into armies and give them objectives. The destruction of planetary targets (weapon control points or ground based weapons and infrastructure,for example) should be one alternative to total subjugation.
(1.1 - Cleaned up extra line breaks. Note to self - do NOT precompose in Notepad!)