I have a simply idea about integrating surface of celestial bodies.
A highway.
The mod adds one more part to the game with super funkcion:
A highway builder. It is one big part equiped with 8 wheels, and two connector balls (on bottom and upper side to connect with your rocket). It looks like a bit oversized ( 15-30m) rover but it can put an asphalt road over places where it get over.
Controling is same as normal rover control with max. speed nearly 20m/s. But it have two buttons, which alow to place a road.
1. Button: toogles between
None,
build mode or
demolish mode
Build mode starts building. None means, you can maneurate without building. Demolish mode clears already existing road and reveals the original terrain.
2. Button determimes the width of the road what appers (or is demolish) after everywhere, where it moves. (Not when flying, bridges in far far future upgrades).
The road looks like 1-10m wide black asphalt zone (you can use original runway texture ) a bit (0,2-0,5 m) over terrain (not water or KSC buildings) to cover all holes and bents with flat area.
You can now build your own runway on duna or highspeed road connecting your mun bases.
We just need a skillful modder, not someone like me.