Having been thinking a bit more over the last few days about how this might work, trying to put actual numbers on it, etc. I think that the additional customisation - energy banks, engines, thrusters, etc. is going to be very difficult to make work without some extremely unpopular sacrifices.
The essential problem - I'll show it with engines, but it applies to the other types of equipment too - is that you need some way to determine whether a ship has a speed of 0.30 because it's a Mamba (small, light) with a light fighter engine, or because it's a Cobra III NPC (heavy) with a much bigger engine. The "obvious" answer to automatically calculate that from the ship's mass falls apart because the mass numbers aren't much use - the Cobra III is heavier than the Boa II. Fortunately we don't really use the mass number for anything other than working out how far you have to be from the main station before you can enter witchspace, some mostly irrelevant calculations for how long a wormhole stays open (usually the wormhole's own mass far outweighs the ships in it), and determining how many hundred times you died in a head-on collision.
So essentially you need to specify something in the shipdata - either override the automatic mass calculation, or add an explicit engine_effect parameter - which says what effect they have. Ships with that parameter can replace their engines; ships without get their speed read in from shipdata and it's assumed that they have a fixed engine that can't be upgraded. Now that's a complete mess - two entirely separate ways of calculating a ship's top speed which also affect its equipment eligibility (and there's no way that "every ship OXP" is an acceptable loss from a deliberate compatibility break, either)
Repeat for thrusters, energy banks, energy generators, etc. (banks and generators are a bit easier, but thrusters are
much worse)
Take those bits out, though, and there's not enough left to make it particularly interesting for a low OXP game: assuming the player sticks with the Cobra III, then there aren't that many alternative configurations available just with the basic equipment set - it just becomes "how close to owning everything do you get before you sell the Large Cargo Bay". Without that, the scope for OXPs to add further interesting decisions is also fairly limited, especially since it'll be a while before any of the existing equipment gets modified to take up space ... and as Thargoid said they can always use hold space directly, and just assume the player is flying something roughly similar in capacity to the Cobra III. The ability to use hold space hasn't exactly caught on much since 1.77 fixed the bugs in it, so maybe there's not that much demand for this.
So ... what does that leave?
- Remove the "optional_equipment" section from shipyard.plist and "available_to_all" from equipment.plist and replace them in the core game with more use of condition scripts. These are virtually useless to OXP equipment anyway.
- Make all equipment sellable, including a configurable sale price, at stations which have the TL to repair it. Pylon weapons continue to be sellable almost everywhere. Need to be a little careful here that selling the initial pulse laser becomes an interesting decision rather than an automatic one.
- Adjust the install/repair/removal times for core equipment items to be more interesting.
- Breakable standard equipment might still be worth considering even if you can't remove it to save space
- Remove the Multi-Targeting System, since no-one spoke up to say it was important to their combat strategy.
- Make equipment damage proportional to attack damage so missile hits really hurt even if you survive
- Introduce 'disrupted' equipment state.
- ECM graphics improvements
- Increase NPC equipment usage and damage
- Advanced Nav Array allows specifying a distant system as a jump destination and automatically updates your route as you travel. I think with the chart improvements kanthoney has made this might be practical. (Intermediate waypoints ... probably not for now - route calculation is slow enough as it is)
- Halve beam laser damage/heat to make it not quite as big a jump over the pulse laser and make fights last a bit longer.
I've bolded the ones likely to make a significant gameplay difference.