Interesting question. Soffit mounting is about making the sound waves coming out of a speaker behave as if the whole front wall was an infinite extension of the baffle. Easy to achieve with a flat-fronted speaker. Acoustically, in principle the 8361 would want to "see" a progressive extension of its waveguide contour, which would be very difficult to achieve. Certainly the examples I have seen (like in your photo) are mounted mostly in the wall, but with too big of a protrusion to be called truly soffit mounted. Thus MF and HF will be taken care of by the waveguide only, but there will be soffit-style benefits in the SBIR region, because the bass slots are only an inch or so ahead of the wall.
How hard would it be to do? Probably a real drag, given the Genelec shape, and that the wall means nothing acoustically, unless it's really solid, which probably means masonry or concrete. Almost certainly not worth it. And not intended - clearly Genelec design for near-wall location, not soffit mounting.