It essentially turns the turbines into gravity powered generators rather than the more normal tilt-motion examples I've seen before. Not a bad idea at all.
I'd be interested to see how it affects tidal patterns when used en-masse - tho' I suppose if moored far enough out the influence would be small. After all, leaching a few hundred MW from the ocean isn't going to make much difference .
However, I still think that the real way forward is local installation photo-voltaic energy. After all, as long as the sun shines, then taking it's energy is no different from what the planet does anyhow.
Wind and wave have their place too, perhaps as 'sumps' for additional energy added into the system from the use of power from other sources i.e. they take out of the waves and wind what other generating plants put in.
This sought of thing is under serious consideration down here in Australia. We have a lot of empty coastline, which is only good-looking not beautiful, to put them on.