Sorry, but this is not necessarily true at all,
and getting security with no energy cost is
quite possibly a pipe-dream.

Proof of stake seeks security without cost,
but the laws of economics say that security
costs will always rise to meet the rewards...

Which has been discussed at length here:
https://bitcointalk.org/index.php?topic=860194.0


...And if you don't want rewards to secure the
system, then you'd be taking away one of
the most important aspects of Bitcoin's security model,
which is incentivizing people to honestly participate
in the network instead of attacking it.

One thing is for sure:  Proof of Stake is a radical
departure from Bitcoin as we know it, and would
necessarily have to start as a fork into an altcoin,
at least to prove the new model, because everyone
isn't going to just wake up one day
and decide they all want to switch over.