Can you explain this, please. An attack happens, someone generates an incorrect chain of 20 blocks. Now, everyone waits for 30 confirmations, so they then see that the fork is invalid and no one accepts an transactions. Why is a rollback or hardfork required?
The consensus algo is what accepts the fork and this is where the weak subjectivity of the users and or developers would need to step in and correct the invalid fork. This has its own set of problems.
I believe Nxt requires a single SHA256 hash for each block. So it already has an element of PoW as suggested there.
This has nothing to do with PoW consensus mechanisms. Next you are going to insinuate hashing itself is "work" thus one should consider all PoS to incorporate the PoW consensus mechanism.
If there is no fundamental reasons why PoW is better than PoS, then PoS will win out due to lower cost (imho).
Yet despite Bitcoin being in a death spiral of capitulation both Bitshares and Nxt have lost far more against bitcoin in the last year. Perhaps there are other factors that are far more prescient than the mining costs to secure the network?
You understand that long range attacks have proven impossible in simulations. So if a bank buys a large chunk of coins and waits the required number of confirmations, then the previous owner cannot launch any attacks. Or am I misunderstanding your premise?
There are many different variants of PoS, and some of them are indeed susceptible to long range attacks. Stop generalizing.