What is fuel? Traditionally in sci-fi gas giants are the fuel depots of interstellar travel. Gas giants are everywhere. Rations in nutripaste form hardly take up any ship space. So in that instance I don't see how WW2 is particularly relevant for interstellar warfare.
STRATEGIC DEPTH
Realism isn't so much the issue as strategic depth and game mechanics. What I would look for are models/mechanics that allow for player response and adds strategic depth. (this is sci-fi, we can make up anything). You can have sci-fi universes where ships go anywhere they like for any distance they like, or are restricted to freeways in space, or are required to restock from time to time on either radioactives, antimatter or hydrogen/helium isotopes or some fake pseudo-science rare gas.
FUEL MODEL
What a "fuel" model offers is that either ships are forced to return to a fuel depot (starbase) to restock from time to time, limiting their ability to advance indefinitely, or are dependent on built technology (cloud scoops) to provide that fuel, or can mine the fuel themselves but it takes lots of time, forcing them to layover for an extended period. This can be very easily added to Stellaris, but more on that below.
GARRISON MODEL
Probably NOT easy to add to Stellaris given its current design, but consider games like CIV or TW where a captured settlement can easily revolt or revert to its previous owners if not garrisoned and subdued for some period of time. Rapidly capturing enemy territory is self-limiting due to the need to suppress revolts, or consolidate the captured territory.
EXAMPLE OF HOW FUEL SYSTEM COULD BE ADDED EASILY TO STELLARIS
Adding a secondary cooldown on the number of sequential jumps a ship/fleet could make would simulate fuel. i.e., if a ship could make 5-10 consecutive warp jumps, but would then need to 'recharge' for an extended period. This 'timer' or 'fuel tank' could be reset when a fleet arrives at a friendly (fully charged?) starbase, or recharge very slowly (from solar power or gas giant or whatever floats your boat) whenever the fleet is idle.
This would make it tricky to operate fleets more than 3-4 jumps away from a friendly starbase, requiring you to build forward staging posts for invasions, or secure travel routes within your empire, without totally trapping or immobilising a fleet. Wormholes and Gateways would still offer you more strategic depth, and the infrastructure to required refuel large fleets would be self-limiting (a natural local supply limit).
EXAMPLE OF IMPLEMENTATION:
- A ship carries 10 units of negative matter.
- A warp jump consumes 1 unit of negative matter.
- It takes 1 year for a ship to manufacture 1 unit of negative matter.
- once a ship has used up its onboard stocks, it would be limited by the rate at which it could manufacture negative matter.
- Starbases manufacture negative matter at a faster rate (say 1/month * level), and can store them in bulk.
- Starbases will restock friendly fleets that dock at the starbase.
GAME IMPLICATIONS
- Surveying ships wont be affected (they can recharge in the time it takes to survey a system).
- Exploration ships will be slowed down significantly once they are 'out of range'.
- Small fleets can be easily resupplied by a low level starbase.
- Large fleets will require a high level starbase to instantly resupply.
- Multiple fleets operating out of the same star system will overwhelm the local starbase capacity in short order (even a citadel).