The a ability to modify ships.
For example, my DBX has a size 5 fsd. If I could modify it, I would change it to size 6, and remove the med hardpoints to make space for it.
Or
Custom crafted ships.
Similar to the other suggestion, it would allow us to be able to create ships using modules, hardpoints, size and bulk the new ship has. For example, I would create a t-8 surveyor. It be slightly larger than the t-7 with a large fsd, a size 8, capable of going long distances, with size 6 thrusters to support the weight. I would also put 5 small hardpoints, and maybe 1-2 meds on it, on it for protection and 4 UM. For the power plant, it would be size 6 to support the fsd and thruster.
Or
Core module booster
It would be an internal module that would boost a core module. For example, o could put a powerplant booster on my alliance chieftain to cover all of the power. Or a life support booster, extending the time of oxygen. Or a thruster supercharger for my imp eagle to increase its boost speed to nearly 1km/s.
Or
Module carriers
Instead of having to transport ships from engineer to engineer for experimental upgrades, I could just take my conda with a few module carriers carrying my alliance chieftain's hardpoints or core modules to an engineer for experimental upgrades.