[PDF]

I like the idea of larger, "inefficient" hull designs at lower Ship tech levels.

It should be easy to implement : for each hull size up to 2 "inefficient hulls" have to be defined, and each tech level could allow "next" hull size inefficient-1 and 2 sizes larger inefficient-2 (more inefficient than 1).
Inefficient-1 will have some 10% less usable space than normal, inefficient-2 15% to 20% less, and perhaps lower speed constraints (larger hulls still have to get more room than smaller one, so a Frigate should have more than 150 Kt useful !)

So for example ship tech-1 will allow :
Escort
Frigate inefficient-1
Destroyer inefficient -2

then ship tech 2 will give
Normal escort and frigate
Destroyer inefficient-1
Lt Cruiser inefficient-2
etc etc

It'll be particularly useful in high start/low progress games such as Proportions.