Proof of Stake modifications
(maybe swap between "Branch selection" and "Cementing" subsections)
Each signature block should also be cemented: once a node receives 50 confirmations following each 100th signature block, it will not accept a competing branch even if the voting weight of the signature block of that branch is higher. This prevents an attacker from preparing a secret forked branch with a signature block that had a higher voting weight, and broadcasting this fork much later (for example, a secret fork that starts at block 500 and is released at block 200,000, thereby reversing 199,500 blocks).
To resolve the problem of nodes which may have been isolated from the network and get locked into a different branch than the rest of the distributed network, there should be an additional option to provide a checkpoint block manually. The node could obtain the hash for the manual checkpoint block from various physical locations, such as newspaper ads, street signs, TV, etc.
To prevent blockchain bloat where anyone with a tiny amount of bitcoins tries to provide his signature at each signatures block, there should be a cutoff rule whereby the miners only accept a signature from an address that controls at least 100 bitcoins, which puts a limit of 210,000 signatures per signature block.