It is quite noteworthy that Ethereum trusts proof of stake so much that they want to move to it though. Ethereum has some really good devs.

Last time I checked for altcoins that are trying to solve Bitcoin‘s various scalability problems I ended up with a proof of stake coin too, Nano (using the rather new idea block lattice, small but so far quite low-toned development team that seemed to focus on problem solving rather than scammy marketing).

I’m surprised that Ethereum is convinced that they can „just move“ from proof of work to proof of stake. Should be possible for Bitcoin too then, shouldn’t it? (Maybe I’m missing something about this transition.) Nano required a whole new development.

Ethereum's social contract has evolved to become much more "fluid" and open to change than Bitcoin's. Mainline Ethereum today is is very different in many ways to what it was two years ago. There is even a proposal with a lot of support to have transaction fees mostly burned rather than mostly given to miners. Aside from minority forks, something like that would never happen in Bitcoin in a million years.

So, while Bitcoin techinically could switch to proof of stake, it probably won't.

Tezos is up and running and working just fine.

Plus Cosmos, Polkadot, Solana, Cardano, Avalanche, NXT, and probably others I'm forgetting. There are plenty of PoS systems in production these days!

As someone who hasn't been watching closely for a while, any thoughts on which of those seem most interesting?

To me Mina and Zcash are interesting since they (plan to) use cryptographic arguments to show that chain states are valid, which leads to some nice features, such as better light clients. I'm probably biased since our own startup was influenced by them. Besides that, I'd say NEAR since it seems like the most promising sharded chain that's in or close to production.

(They weren't on the list since Mina hasn't launched quite yet, Zcash isn't PoS though it might switch, and NEAR isn't PoS in its current form, but will be soon.)

All of those are run by a singular entity. This makes it trivial for them to implement PoS.

That's not the use case something like Bitcoin is built for.

That's flatly untrue.

How can that be controversial? They all had an ICO to begin with. Some of them have even registered a company or organization to back it up.

The controversy is in the language "started" vs. "run."

Tezos, as an example, is governed by voting and on-chain governance. It isn't "run by a single entity."

Ripple or Tether are, though, sure.

Governance is more than a voting protocol. Tezos is not governed by equal actors.

There is a "Tezos Foundation". They control 30% of all staked XTZ. They checkpoint the blockchain regularly to provide correct history.

It seems to me that admin rights to the bitcoin core github repo count for a lot more than a 30% vote.

You can make near-zero-cost ETH and ERC-20 transfers right now using L2 solutions like state channels and rollups. There are also a few POCs of applications like Uniswap running on L2.