Earlier quoted context omitted.
I would argue they already did achieve large scale trust, based on how many billions of assets are traded on the network.
The whole point of a public blockchain is for it to be trustless. Why do you even need to factor in achieving 'Large scale trust' with the largest Ethereum stakeholders to not say, attempt to revert a massive hack in 2016 to save the investors lost money? Why should I have to trust them to not do that again if another hack happened, even if they migrate to PoS and it causes a giant fork once again?
A public blockchain is supposed to be "trustless" in that you don't have to trust humans to be honest, because the system is harshly fair and enforced by computation and the laws of physics that no one can trivially bullshit their way around. The important function of proof of work is that it solves the Byzantine generals problem such that everyone can trust the system without caring much about who else is using or controlling it.
Proof of stake is problematic because it shifts the burden of trust back into the hands of humans, and we all know that "the hearts of men are easily corrupted".