This is an example of an approach to smart contracts that uses the Stellar model which keeps the bulk of the logic outside of the system so only people that are interested need do any processing. This should make it more scalable.
I haven't thought through it yet but I think the most common case would actually be 1 directional. Curious if people agree or have another opinion?
Didn't stellar's PoS network fork?
The Stellar network did fork when we running on a fork of legacy software. Since then, we have rebuilt the entire consensus system using a completely different consensus system. The underlying consensus system was designed by Prof. David Mazieres, head of Stanford University's Secure Computing group - you can read the white paper here: https://www.stellar.org/developers/learn/concepts/scp.html A completely new implementation of SCP in the form of stellar-core was completed earlier this year. You can read about it here: http://graydon.livejournal.com/227874.html