Yes it can be done... however there's certain limitations.
1) works best with AC currents; with DC you can get it inverted to AC but this then becomes very inefficient.
2) generally for the higher voltage stuff that calls for voltage-multiplication ladders, there's very low current draw and not meant for the high ampereage what our DC motors call for.
So its all a toss-up between what you want from your RC. If you just want higher voltages for higher speeds... why not just campaign for 7-cell (or more) racing??
And it *is* already done today... ie voltage amplification in RC.
Just check out a Tomy Bit CharG (aka Hobbyco Microsizer). These things run on a single nicad 1.5V cell, but some parts of the RF circuitry require 3V to run.