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.