You keep mentioning tardis cargo racks, but the ships as they are are far larger than their cargo capacity. A single unit of cargo is a 1x1x2 meter capsule, and the ships are absolutely enormous compared to that, they can physically stock thousands already. If the type 9 was a perfect brick, if would have 449,402.504 m3 of volume, compared to the volume of its max potential cargo, 1580. Lets knock off 50% of that volume for it not being a perfect brick, the ships hull, internal modules, passageways, sleeping quarters, etc. Now our half size is 224,701 m3, and 1580 m3 of that is only .7% of the space. By volume, the T-9 can with this extremely conservative and rough cut number hold 112,350 tons of cargo. So, obviously, cargo volume isnt the restriction, there is no tardis situation.That's how it begins.
Remember the first SCO drives? Only E, plain.
Then soon, slowly, introduced all classes, then the possibility of engineering, then the magic ones from Titan elements...
That's how my Tardis cargo racks will develop - all classes, for all the ships, with no ship preparations - just with a caveat: in them, only cargo and fuel.
Clearly, in universe, if we wanted a better cargo ship, a larger FSD and Engine cluster would be designed. Mass has always been the issue, not volume, So not giving the PC a new class of FSD and engine is just lazy, in and out of universe.