The position seems to be that it will continue to work for the time being, so there is still time for more research.

Proof of stake has problems with handling long term reversals.  The main proposal is to slightly weaken the security requirements.

With POW, a new node only needs to know the genesis block (and network rules) to fully determine which of two chains is the strongest.

Penalties for abusing POS inherently create a time horizon.  A suggested POS security model would assume that a full node is a node that resyncs with the network regularly (every N blocks).    N would be depend on the network rules of the coin.

The alternative is that 51% of the holders of coins at the genesis block can rewrite the entire chain.  The genesis block might not be the first block, a POS coin might still use POW for minting.

https://blog.ethereum.org/2014/11/25/proof-stake-learned-love-weak-subjectivity/