The the way you explain this, Alain, seems to me the same as potential energy. So vacuum has some energy in excess to its crowded and full of particles surrounding area. If mass is energy, than I would say that vacuum has a lot less energy than matter. It seems not right to me. But:
Assume a black hole. In the centre the mass density is infinite, when looking at it from our universe. Looking at it from the other side, there will be a totally empty space at the same vicinity point. Maybe the more empty vacuum is the nearer you are at the black hole and the more energy there is. How do you think about this view?
About the theoretical production of Mr Geneste, as it is formulated, and accounting from his past books, I feel it is much more general than proposing Weak Interaction, or BEC theory...
about vacuum energy I have watched discussion on that concept with emDrive.
My impression is that Vacuum is like the basic quietest state of a lake, not even a lake, but the perfectly still ocean.
you cannot get energy from the ocean quiet state, but from excited state like from waves, from thermal gradients.
you can see there is huge mass of energy as stored in ocean quiet state, in ocean pressure, in gravity, it seems huge but you cannot do anything with it, as there is nothing lower.
On the opposite you can swim in it (that is what some propose for EmDrive), or catch energy from waves caused by excitation of that still system.
Some like Michael McCulloch (and Unruh) propose that presence of objects in the ocean change the quiet state and allow some action, especially because the lowest energy state of quantum ocean is not perfectly still.
an example is a strange effect observed in ports. when there is a basic wave presence in a port, there is a spontaneous effect that make boats get toward the pier.
it is a casimir pressure, because between the pier and the boat only few waves wavelength are allowed, and that on the opposite open sea side there is much more wavelength allowed....
This is not a free-lunch energy, but it may be useful.