I have played a bit with ship design, and here are some thoughts:
- as noted in the bug reports thread, you don't see anything when trying to upgrade a design you have made. But if you copy the ships files in the same directory than the predefined ships, you will see teh ship
- as noted in the bug reports, when trying to do an upgrade, sometimes you can't add or remove any components
- you can't duplicate a ship design. Which is a bit annoying if you want to have few ships that can be buid at the same time but are based on a similar design
- upgrading a ship means that you lost the previous design
- you can only rotate the ship in 3 axis, you can't translate it, meaning that sometimes you will have lots of trouble to select a mounting point
- you don't have a way to know/see all the designs you have already made in previous games (even if if required tech/miniaturization level aren't meet yet). So you can end overwriting a design without knowing it
- I was playing the Thalan. But the predefined constructor and freighter were based on the human cargo. And the predefined freighter is a bit unbalanced: when you update it, you find that you have lot of space: it seems to have the trade ability without using the associated space.