Reality is, can it be done? Yes it can and many do it and many have been doing it for years.
Will you get the full torque out of the servo this way? No, there will be some voltage loss due to the connections used on servos and receivers. That being said today's servos have more than enough torque to exceed the demands we put on them.
There are those who live and die by power supply and weight savings and there are those who don't and both still fly the heck out of their planes. I personally have Y on my 4 8611s in my H9 35% 260 in the wings and can 3D it with the best of them. It snaps crisp and stops when I want. Would be it even better with a power expander? Yes the extra voltage would help a bit but it flies just fine the way it is.
You need to take all the input on this topic with a grain of salt. Many have been flying Li-ons packs for years with limited burst availablity without any issues and the sky wasn't falling before A123s came out
