I had an idea a while back that may be relevant. Basically, I was thinking "How could you have a multiplayer game where people can play the same empire offline and not bash everyone else?" My conclusion was similar to Terraria, world-hopping. The game (would have) consisted of two major parts. 1: You own a mothership, no colonies. Your mothership is a refinery, shipyard, residential sector, research lab, everything, and it's jump-capable. 2: You jump a lot.
How it (would have) played, is that you start the game. If you're in single-player mode then it drops your mothership into an asteroid field or somesuch, allowing you to send mining ships to retrieve ore, with a small delay until some NPC arrived and gave you trouble. It ended when you left, with ever-increasing enemy waves forcing you eventually to retreat. Of course, surviving longer meant more time to harvest debris and perform research, from reclaimed vessels, your own tech, and observing combat (like watching how plasma reacts and learning how to control it by practice). Then when you're done, you warp away. Your mothership is saved separate from the world, so when you want to play again, it loads up a fresh map and lets you explore a new area to abuse. Some places would be harder and more rewarding, while others a bit softer, allowing you to casually collect scraps of ore and perform maintenance.
Then when you want to play multiplayer, it loads your mothership and assets, and places it into a larger map, with yourself close or far from the other players depending on the setup and/or teams.
The advantage of this is, obviously, portability of play, and centralization of resources. You don't get a dozen colonies, you just get your mothership which may be advanced enough to perform like a dozen colonies would. This is significantly easier on the CPU (or the calculator and pen), and allows for some more freeform playstyle. For my idea, it would have been limited to a few active fleets at a time, so you wouldn't have twenty fleets moving about, you might get a cap of 3-4 for mining and defense and offense and diversionary offense. The downside, is that it doesn't feel very 4X, it would play a bit more arcade strategy in the vein of starcraft rather than your spanning empires in Sins of a Solar Empire. It also puts a lot of emphasis on the one mothership, although in my thinking it would have some hefty armor. You'd have enough time to escape an enemy, probably, but you'd take some damage while the engines warmed up, some punishment for being forced to retreat. And of course the mothership could be outfitted as an economic beast to field a big fleet, an orbital drydock to spam fighters faster than they're destroyed, or just layer on the armor and strong-arm your way through the enemy fleet using a custom dreadnaught. My version of combat was rather advanced, with several layers of missiles and anti-missiles and armor and shields and EVERYTHING factoring in, but it was for computer so you could bare-bones it for calculator.
...now I want to start coding again D: