I'd like to see a very few of the old ships be included, sort of how we sometimes see people driving pre-WW2 cars or several 'classic car' models. They would have to be kept to a minimum and controlled somehow (maybe generated randomly but rarely in Shipyards, or offered as rewards for special missions). As they are so rare upon ship destruction the pilot is placed back in a Sidey immediately as no replacement is available (so their rebuy value is N/A).
Obviously, this would need to be a labour of love on the part of FD to design them and place them in game, over and above their stated intention to provide 30 playable ships. Consider them akin to Easter Eggs in movies.