See, this is one of the big problems with Proof of Stake.  There will forever be a block that shows a large stakeholder as having that huge stake.  If you go for checkpoints, not only do you likely lose your decentralization, but now you are saying every block after the last checkpoint cannot be trusted.  You are in effect saying we need to wait for a block to be incorporated into a checkpoint to be confirmed.  This means a) true confirmations take a very long time, and b) this network isn't very decentralized.

There is no way to go back in time in a Proof of Work network and reclaim the hashrate you had to confirm a new block.  All Proof (Work, i.e. hashrate) must be made new as it is based in the real world, and not on something in the blockchain.