There has to be a few million GPU miners in the world. Why has no one built specialized equipment? Mobos that can run tons of cards, PSU with lots of power adapters. I'm sure a GPU could be modified to hash faster than a general GPU. Of course it would essentially become an asics market so forget I said anything.
That is too theoretic
There are some known attempts with more or less success. You can find them here on bitcointalk from the past few years.
I think the answer to your question is that:
1. Yes, it is that much hard, that not many can do it. Also special (internal) hardware/software is required to do it.
2. Details are not made public for obvious reasons.
jstefanop leaked some info on his new hw/sw solution that will be available soon.
