Don't know if someone has ever talked about this subject.
I've seen in the Stewart Components web site their integrated cooling approach, and asked myself if it could be used in WC.
A concept like Sanyo Denki that features a very small pump is also a candidate:
As pumps will get smaller, no doubt following the recent trend (Laing DDC), one would avoid pressure losses from tubing, possible cavitation and the use of a reservoir and the pump would work as efficiently as it could.
What are your opinions on this?