To expand on this, as this part of burstcoin is inherited from NXT, a comparison is possible.
You see documented here somebody describing something that could be similar to this, but sadly they never revealed the details as they wanted a bounty first and were rather alarmist about things.
However, in practice, you would not see this on NXT as:
- The coin is fairly well distributed compared to the historical and potential size of pools in burstcoin. Pools never really took off in NXT to reach the percentages they have in burstcoin.
- Even though the largest coin balances would allow for something similar, with transparent forging implemented the disruption possible through doing this is eliminated and attempting a double spend appears to become infeasible but I won't claim to know NXT well enough to say for sure. Transparent forging is a PoS concept and not applicable to PoC.
- A 1 minute block time increases the number of blocks an attacker would need to win a row to perform a double spend after the same amount of time, further reducing the ability to take advantage of this.
In many ways this proposal is similar to transparent forging - rather than predicting who will generate a block in advance, allowing this to be distributed and penalising and ignoring forks based upon this, this proposal requires miners to decide upfront what their block will contain and as recomputing the PoC data isn't possible in real time this is just as good as being able to predict and anticipate the chain. Note that NXT's description of transparent forging also includes similar estimations of the difficulty of double spends with a technique such as this in place as in the linked github PR.
Ultimately PoC is closer to PoW in nature than PoS, hence the need to include the block contents to ensure reliability and prevent rewrites of the chain to create forks for double spends.