You won't see a Nikon or Canon with a Foveon sensor because these
sensors don't have the resolution or ISO range of the other sensors that
are available. I don't think its anything to do with Foveon being a U.S.
company.
The fact of the matter is that the larger the silicon chip the more expensive
it is to produce. You can only fit fewer of them on a silicon wafer. The
larger a sensor the more failures you are likely to have in production and this
also drives up the cost.
Only the quest for more pixels and lower noise might drive the camera
makers to full 35mm size sensors.
If this company can actually produce some sensors then the camera
makers will look at them because they aren't stupid. But an idea for
producing a sensor and actually producing one economically are two
different things.
Look at Contax's attempt to produce a camera in the N1 body with a full
size sensor. They couldn't get the usable ISO above 400. The whole
project was an expensive failure.