capacitors et all
I've designed boards that are liquid cooled,
all the boards are in a big box which is filled with a pink silicon type liquid, and the box closed.
Yes there is room for expansion, and the walls of the box have water flowing through them to conduct the heat away.
any oscillators / crystals need special attention
the impedance of the tracks on the surface of the board are different to being in air.
( but as there is no dust / skin cell build up over time, at least its possible to calculate )
Capacitors not a problem, if you use the right ones.
The most common capacitor is a ceramic, and most of them are fine,
When it comes to analog / rf, then things are a little more difficult, the fluid does tend to kill them,
but digital is just fine.
it does make the thing REAL heavy
and once a board has been in the fluid for long, its impossible to solder to it ever again,
the fluid just can't be cleaned off sufficiently well to make a good joint,
For 'fun' one time, we ran one of the boards in liquid nitrogen,
now that was cool, but we dare not seal the box !!!
Will it catch on at home, I don't think so, but some of these real small PC's that fit in the hand might be interesting in a sealed box full of liquid.