I've been working with jl2012 on some SEGWIT BIPs based on earlier discussions Pieter Wuille's implementation. We're considering submitting three separate BIPs:

 

 

CONSENSUS BIP: witness structures and how they're committed to blocks, cost metrics and limits, the scripting system (witness programs), and the soft fork mechanism.

 

PEER SERVICES BIP: relay message structures, witnesstx serialization, and other issues pertaining to the p2p protocol such as IBD, synchronization, tx and block propagation, etc... 

 

APPLICATIONS BIP: scriptPubKey encoding formats and other wallet interoperability concerns.

 

 

The Consensus BIP is submitted as a draft and is pending BIP number assignment: https://github.com/bitcoin/bips/pull/265

The other two BIPS will be drafted soon.

 

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Eric