I don't mean add new type of parts. I mean a set of parts which are consist of stock parts such as some fuel tanks or so. The idea is a little like the custom subassembly. But I want to have the similar part sets in the part list already in stock game, which I don't need to make by myself. They can be SRBs ,antennas, or even a premade mechanical arms which made by the stock parts. Sometimes when I start the game and I will have no idea to build anything. I just want to build a rocket just like playing Lego but not modeling. The game has already made some prefab parts such as career payloads, new propellers (connected propeller to electricity motor), but the game can do more. I think it can not only lower down the boredom of building, but also make the part lists larger. And that maybe not so difficult to make than make a new type of parts (Yeah the 1.1 propeller is new type of part and it took a long time to develop)
good