True. But the same counts for planes if they stall, the trick is to avoid stalling by specifying the correct design envelope for the foil. Generally speaking, the larger the foil and lower the aspect ratio, the less likely it is to stall. Large foils would be very prudent on this thing, less likely to stall and would provide an amount of bouyancy at slower pre-foiling speeds. The size I envisage off the top of my head for a 40' (similar to the sketch) would be about 4m chord, 10m length, 0.3m at thickest point and about 10m span between foils. This is for both bouyancy and height "control" in waves.

Personally, I don't think it is feasible, you may as well have a trimaran with banana boards, much safer.

Looking at the 60' tris going around atm though, it looks as though they are converging closer to the concept design. Less outer hull volume on the tris (for less windage) with larger banana boards seems to be the trend, if it is class legal. At the extreme range of this trend is the dihedral foiler monohull...

As the tris continue on this trend they will find a happy medium, which probably won't be as extreme as the concept monohull.