I can`t use english well.... but I suggest something.
About capacity of FuelTanks.
Formerly you tell that reason of low capacity of fueltanks is it is designed for aircrafts, but I think OPT`s parts are good for spacecrafts TOO.
I want you consider about to raise capacity of fueltanks.
Heavy weight of fueltanks with high capacity can be solved in player`s discrtion.
(We can adjust loadage of fueltanks in SPH or VAB)
If you accept this suggestion, OPT will get more possibility
And...... wil you add J inline docking port again?