MIA Coin and NYCCoin use PoX as part of their fraud. Harvard Management Company perhaps has a hand in the scheme?

PoX when used for participation rewards, as described, could lead to miner consoli-

dation. Because miners that also participate as holders could gain an advantage over

miners who do not participate as holders, miners would be strongly incentivized to

buy the new cryptocurrency and use it to crowd out other miners. In the extreme case,

this consolidation could lead to centralization of mining, which would undermine the

decentralization goals of the public blockchain.

Bitcoin Bandwidth:

Because PoX miners must send Bitcoin transactions to participate in the consensus

algorithm and send PoX rewards, PoX mining would occupy some Bitcoin transac-

tion bandwidth. Given Bitcoin bandwidth is limited by design, given security require-

ments, new PoX blockchains need to reduce their bandwidth use requirements. SIP-

007 does this by limiting the number of participants, using a STX holding threshold.

Other ways to address bandwidth limitations are also possible e.g., lighting channels

between Bitcoin and the new blockchain. Optimizations at the Bitcoin transactions

layer could also be possible, which would reduce the total size needed for PoX trans-

actions.