I have heard of people trying to build analog AI devices but that seems like years ago, and no news has come out about it in recent times. Maybe it is harder than it seems. I bet it is expensive to regulate voltage so precisely and it's not a flexible enough scheme to be support training neural networks like we have now, which are highly reconfigurable. I've also heard of people trying to use analog computing for more mundane things. But no devices have hit the market after so many years so I'm assuming it is a super hard problem, maybe even intractible.
Perhaps another variation on the idea is to allow a higher error rate. For example, if a 0.01% error rate was acceptable in AI, perhaps the voltage range between states could be lowered (which has a quadratic relationship to power consumption) and clock speed could increase.
