I would like to see procedural engines because:
I think that it would be educational not just do you have to choose an engine from a list
do you want it to be optimized for atmosphere or space
do you want presser fed or are you willing to weight/cost consequence of larger more efficient engines
I would like to see procedural fuel tanks because:
it is silly that some of the shapes and sizes that are only available with certain types of fuel, at least being able to change the cargo content would be a big help.
having some procedural tank would also reduce part counts and make the game run smother, compromise could be the ability to fuse part in the editor