Meni's hybrid Pow PoS proposal seems great.
Has this been implemented in an alt?
What aspects of it can be implemented in bitcoin without a hard fork?
It is generally accepted that any crypto coin that uses mining algorithm that is not pure PoW will not be considered "Bitcoin". This is true even if "Bitcoin" forks into something else, if PoW is not exclusively used, it will no longer be Bitcoin
perhaps.
ultimately it is what users want and agree to.
but I think adding some poS checkpoints a la Meni
is a far less radical change than many other proposals.