Thank you for pointing out that the users of bitcoin (and other cryptocurrencies) have effectively no say in the design of the system they have to trust. This will ultimately limit the very trust needed to keep it alive IMHO.
Besides the other response you received, there also seems to be a shift to PoS simply because PoW mining wastes a lot of electricity.
1. Politics. Ethereum has a leadership team which functions very differently from Bitcoin Core. For one, the creator of Ethereum is well known and outspoken. He and the other members of the Ethereum Foundation made it clear that their intention was always to move to Proof of Stake. Though there are some who may not support this move, the general community bought into the project knowing that this was the plan from the beginning. And there's a lot of trust of Vitalik.
2. Technology. Ethereum adapts much more quickly to mining difficulty than Bitcoin. Bitcoin can't survive with 90% of the hash power on one chain and 10% of the hash power on another chain. The smaller chain would take 10 hours to mine a single block and months to readjust the difficulty. It would be unusable. Ethereum has already shown its resiliency to a split during the DAO hard fork. The smaller chain adjusted quickly and survived. What this might mean is that with the change to PoS, there could be a dissenting faction that remains on PoW, and both chains will survive. This will allow the PoS chain to go ahead and push through with a split easily even without 100% support.
how is that any different to the existing currency system like credit cards and banking?
And users _do_ have a say in bitcoins. Namely, they can vote with their wallet (literally and figuratively).
Fiat currency is governed by central banks, which are arms of government, and are accountable to the public in the same way as the issuing government. Obviously, the degree of accountability varies from government to government.
And I say that as someone who voted Remain in the Brexit referendum (note that Varoufakis actually campaigned on the Remain side in the UK).
It's roughly similar to buying shares in a publicly-traded bank, which you can do as well as electing candidates for public office to whom the central bank, which is the entity making monetary policy decisions, is accountable.
So it gives you more relative power with altcoins only to the extent that those with more wealth are relatively uninterested in the altcoins in question compared to traditional banking; were a digital currency to succeed beyond a small niche, that would change and you would find yourself as drowned out by moneyed interests as you are in traditional banking on that avenue of leverage, and without the other avenues of accountability that exist with the governance of fiat currencies.
i dont believe that even owning a bank could you directly control monetary policy or procedures that the gov't legislates. You'd have to own either the majority of all banks, or own the gov't yourself (i.e., dictatorship), and even then, it's a hardsell.