it's a very interesting prospect and my first thought was flashflood by nanostate
It would require fully dismantling the device which is difficult in itself but I doubt this would work on a whole macbook anyway because the screen would be hard to coat properly.
dismantling a macbook ain't an easy task!
Then there's the issue of how the heat generated by the processor and components would affect the coating, it could well negate the protection or worse damage the parts.
And much like the previous answer the fans would be an issue the moment submersion occured because water is far more viscous than air so they'd burn out or be serious damaged by the water.
In regards to the point made about mineral oil submersion, this is totally possible because of the nonconductive nature of the chosen oils. Amari made this amazing fully submerged custom pc that used fluorinert and I remember reading about how hard it was to find pumps powerful enough to push the liquid around, once fully loaded the computer weighed something like 100KG!
So really a conventional laptop isn't something that could be easily made waterproof however because of the nature of ultrabooks using super low power processors it's only a matter of time before Apple release a Macbook Air without vents or fans making this a more feasible idea! You can guarantee the Liquipel guys will have attempted this or will in the future as no doubt there could be a lot of money to be made in waterproofing a laptop, I say this as I'm sitting outside and a dark rainy looking cloud looms above haha.