Initial thought is I don't like it. There's nothing special about the weight being attached to the generator unless that weight serves double-duty saving cost or reducing complexity. The video didn't mention anything thing about that. As it is, looks like a more complex thing, and no explanation of how the design would reduce the LCOE (Levelized Cost of Energy).
Also, water is way more dense than air, so having the weight underwater is a disadvantage as far as efficiency is concerned. Those weights would be pumping enormous amounts of water as it gets displaced with movement.
I put this in the category of kite wind turbines.
