Why would you need to reduce the size? If it is available early, but requires more crew and has a poor ECM hull rating, no worries.
I don't think you need to name the hulls that strictly, either: "Excelsior" is a class of ship, not a hull size.
You could encourage the use of hulls with newer images just by continually reducing the crew requirements, improving the base ECM, and basic supply/cargo storage.
Even if the ship is smaller, players will choose it for the side-effect advantages, and just build more of them
