Am I right that algorithms/concepts/networks like PBFT, ripple and hyperledger all fall into the same category in so far as they all suffer from being either not open (=the participation (as a node) in the finding of the consensus depends on the decision of a centralized entity) or if everyone can provide a node they suffer from sybill attacks?

Links:
http://www.coindesk.com/stellar-ripple-hyperledger-rivals-bitcoin-proof-work/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+CoinDesk+%28CoinDesk+-+The+Voice+of+Digital+Currency%29

http://hyperledger.com/

http://video.mit.edu/watch/practical-byzantine-fault-tolerance-9388/