Nano claims to do it in action. So do others. Some of them might even be proven right, the vast majority will not, so acting like it's some kind of trivial solved problem is disingenuous. Ethereum's PoS has been in development for years and there is still no consensus that it will be a better mechanism than PoW.
> acting like it's some kind of trivial solved problem is highly disingenuous
I said it's possible. I didn't say it was easy. That said, PoW on a small scale is an interesting experiment. On a large scale, it's a horrible way of allocating energy usage. So while the databases running on PoW are working, they are a stupid waste of energy.
That's like saying space travel is a stupid waste of energy because it costs more than driving. Some things are expensive, sometimes they get cheaper. In the meantime if you want to get to Mars you either buy the proven rocket or the cheap one.