[X6S1x6Okd1st]

You are right, the security of the chain should always be proportional to fees paid.

The security of any given transaction is a little different. In practice we haven't seen that many double spends against chains that are defacto vulnerable (e.g. any chain that uses the same PoW as bitcoin is always vulnerable to an attack).

Assuming that PoS goes well for ETH it might make sense to start moving away from PoW coins before the fees drop to worrying levels.

[rcxdude]

It seems quite unlikely for bitcoin to successfully change anything about the protocol: even simple changes have been failures.

[rodiger]

As of right now yes, but when there are more stakeholders and clear/imminent threats to the chain there will likely be more discussion. All proposed forks thus far have been unnecessary for the short-term success of the chain.