Sorry, but limpets, fuel scoop, cargo rack and whatnot in a combat ship make no more sense than the 3rd and 4th seat and a bicycle rack in a racing car.
And being able to put up a real fight in trader ship against a specialised combat ship is something like racing in your family van vs a F1 car, or fighting in a truck against an M1 Abrams, for that matter.
Gameplay trumps realism. If you must latch on to realism, then look back to the age of sail where a trade ship very well could be packing cannons, and certain kinds of cannons were even sold specifically for this purpose.
If you're doing combat missions, chasing down a target, using plasma slug munitions, or just generally moving around, a fuel scoop can indeed be very useful, especially considering the anemic range of some combat ships. Limpets are very useful for collecting materials dropped from downed targets. Cargo space and limpets are critical to doing actual piracy. Repair limpets can be useful for keeping a ship patched up between skirmishes in extended sorties (or at least conceivably could be, pending balance tweaking). An SRV can be helpful for gathering synthesis materials, as well, for rearming without needing to return to a station. Then there are of course the bounty and wake scanners, and cargo scanner if you're looking to liberate cargo. Many other modules could be added in the future for combat-related careers, as well, such as the aforementioned prison cells, modules to give you more max ammo. There are plenty of modules a ship can currently carry that assist with combat career efficiency, and many more that could conceivably be added in the future.
Taking pretty much any of these is foolish
now, but that's only because of the substantial amount health you have to give up to do so. Many of those modules aren't relevant specifically for exclusively fighting and killing other players, but that's an small sub-specialization of "combat" as a whole, and even of PvP potential encounters. If my proposed changes were implemented, you could still choose to leave all your optional slots empty if you really wanted to. It would potentially save you a bit of weight and power, and give you a slight edge against a more loaded ship. You would, however, have the
option to bring a slightly more broadly capable vessle, without significantly gimping your chances in a fight. Who knows? Maybe we'd see a few more people looking into piracy if they could bring the gear required to do so without trashing their combat readiness, relatively speaking.
The point is to give options without having to gimp your ability to properly fight, which is the only activity that can potentially be thrust upon you. You don't have to worry about all ships being able to bring a full mining build, because you don't have to worry about someone interdicting you and forcing you into a mining race...
to the death. At any point in time, however, (with the exception of deep space exploration), another ship very well could interdict you and force you into a combat situation. The only way for those sudden situations to remain interesting for all parties, is if all parties can remain equiped for a fight, even when they're not looking for one.