Fuselage Tubes with rounding radius or Custom procedural parts.
What we really need for making detailed fuselages with interiors: ability to make empty inside fuselage blocks in a couple clicks. New part or as option for current fuselage block - no matter. As additional options to tubes we need adjusting rounding radius, may be even placing rounding point on specific place of fuselage parts. Also, for tubes, we need ability to choose wall thickness in 4 places.
There is another way, more complex, but it opens huge amount of opportunities to all users. Custom part. When you use it you can build any shapes by determining where and how next piece of that part will turn(sizes, turn degrees, connection types, rounding radiuses, e.t.c.). For exemple, you make a first point of custom part like common fuselage block with 0.5,0.5 on sides and 0,0,5 offset, then place 2nd point with same parameters 2 unitst up and left, and telling designer that you want roundet connectiont type with 1 units radius, then we place 3rd point 2 units up and right with same parameters and connection type, 4th point 2 units right and down and connecting it with 3rd and 1st points. Now we have tube as one single part. No more 0.1,0.1 blocks insane 2-5 degrees rotating and detailed fusleages from 100+ parts.