What i'm thinking is that when two elevator blocks are placed directly below each other, then it will double the capacity in which a elevator can pass through block.s

So they get double the reach to the next elevator. giving it 40 blocks, when it previously could only pass through 20 blocks.

I know this is configurable, but my idea is make it an in-game choice rather than config choice for servers

That would be neat. Thaumcraft's elevator thingy works like that, and it would allow people to try new things. Making it so that it is a 1:1 conversion might work, because it cuts down on how many times you need to press space, but lowers the amount of times you have of floors.