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