Werbil -
Yes, I am aware that water scooping has been done for many years using float equipped aircraft/flying boats. I'm aware of the Fireboss 802.
However the way I see it is this:
If the aircraft is planing on the surface, scooping water, and is subject to a subtle disturbance, then the difference between using a water hull and skis is that the hull's increasing displacement as it lowers in the water results in greater buoyancy, forcing the aircraft to pitch up. It is therefore a stabilising force.
Whereas if the skis are lowered further into the water, there is a significant an increase in drag (below the cg), there is no significant increase in buoyancy, and although there is some hydrodynamic lift produced by the skis, I would view it as primarily a destabilising situation (i.e. nose over into the water).
In regards to the drag load being behind the c.g. preventing a water loop, this is true for lateral stability yes, but does not affect the longitudinal stability issue (i.e. nose over into the water).
That's why they have been putting scoops on floatplanes and flying boats since the 1950's, but by 2008, only Col Pay had been trying it with skis (unless someone knows of some other examples). Any water-based ski-equipped/hydro-foil equipped aircraft? I can't think of any. I suspect for the same reason - too unstable!