The problem isn't the size, its quantum mechanics taking over. When you have two conducting paths running in parallel of each other and the distance between them is less then the electrons gyro-radius, then the electron can and will tunnel for one conductor to another bypassing anything in-between. What people must realize is that molecules are full of empty space, lots of empty space. Electrons are very very very small, they easily fit inside the empty space of every atom in the world. Typically electrons have no desire to do this and will follow the path of least resistance using EM laws. Electrons don't more in a straight line, they actually are spinning in large circles based on how much energy they have. More energy (voltage in this case) means larger circles. It has proven impossible to control the exact position of an election, you can just control the approximate position by forcing it to move in a direction and thus control the center of its circle. If the electron has multiple paths available that are within its circle, then it can and will jump to whatever path has the least resistance at that exact moment in time that the electron pass's near the second path. To an observer it appears that the electrons charge jumped from one conductor to another without moving through the intervening space.
Electrons are basically always tunneling through all mater, it's just a very predictable movement.. usually.
So yeah to get down to 9nm, we will face a choice of insanely large amounts of unused die space (9nm lanes but 15~20nm spacing in-between), or insanely low voltage (0.5~0.8v). Low voltage will make getting high clock speeds difficult, wasted space will increase price. Pick your poison.