Luke,

Eric Lombrozo is doing work similar to that. You may wish to connect. 

He's building a BIP to standardize a multisig application of BIP32. 

Like there are xprv and xpubs for single keychains, he is developing a similar construct that would embed all information necessary for a "multisig xpub" (total keychains in system, minimum # of keys required, and which derivation paths on each keychain are to be combined to make the resultant multisig wallet)

The result would be taking an xpub style string and piping it through a BIP32-like algorithm to pop off P2SH addresses in a deterministic order, just like BIP32 pops off standard addresses in deterministic order. 

I will ping Eric to connect with you in case the both of you are working on something similar and you can help each other.

On Thu, Dec 4, 2014 at 7:42 AM, Luke Dashjr <luke@dashjr.org> wrote:

Is anyone working on a serialisation format to convey P2SH HD chains? For
example, to give someone who wants to make recurring payments a single token
that can be used to generate many P2SH addresses paying to a multisig script.

I'm thinking of something along the lines of a simple series of tokens, each
indicating either a HD chain or literal script content. For all HD chains in
the data, a child key would be generated based on the payment number, and all
tokens concatenated to form the P2SH serialised script. Eg, for a simple 2-
of-2, you would do something like this:
   literal(OP_2) HDChain HDChain literal(OP_2 OP_CHECKMULTISIG)
Does this sufficiently cover all reasonable use cases?

Luke