You CAN put foils on anything, the real issue is SHOULD you put foils on a particular type of boat.  Proas are designed to change bow for stern while shunting, and the foils on the boat have to deal with this frequent change.  This makes adding lifting foils a lot more complicated than in traditional unidirectional sailing craft.

Proas attain their speed and efficiency through narrow hulls, light weight and relatively powerful rigs due to the high righting moment from the wide spacing between the vaka and ama.  This "formula" for speed works well and is both cost, structurally and material efficient.

Adding lifting foils adds stress and structural demands that forces the basic proa design to become tremendously more complicated with higher cost materials and sophisticated engineering design.  And then you add the very high expense of multiple lifting foils & control systems.

Although lifting foils can add incredible speed in optimal conditions, boat like proas aren't sailed on one point of sail on perfect days where the wind meets the requirements to foil.  My point is that for 90% of the time you are sailing a proa, lifting foils would be a liability not an asset.  Upwind? I doubt lifting foils would help.  Straight downwind? Nope - no foiler can foil going straight downwind.  Low wind days?  Foils would just be a literal drag.  High wind days?  Foils could quickly become uncontrollable due to ventilation and cavitation.

The though of quietly blasting along on lifting hydrofoils is very seductive and makes for good dreams.  The reality of living with paying a lot more, restricting your sailing to perfect conditions and being slower than other boats for a lot of your sailing time makes the dream impractical for me.

I watched firsthand Fred Eaton and Steve Killing's first attempts to build a foiling C-Class competitor.  It DID foil but it wasn't able to be competitive with their non-foiling C-Class race boats over the complete range of race conditions at the time.  They mothballed their first foiler and won the Little America's Cup with their displacement hull C-Class cat.  Subsequently foilers have become the C-Class standard - but C-Class cats do not have any of the design complications that shunting proas do - and they are pure race boats sailed only in competition.

You CAN put foils on a proa, but SHOULD you?  I think putting lifting foils on a proa "breaks" the magic formula of high speed, low cost, structurally efficient design and simple operation across a wide range of conditions.  My opinion only - everyone gets to make their own decisions.

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