I have fixed the feed publishing, and tested against the latest development version of piston.

Will be releasing it in a new module in steemtools next week. For anyone interested, the updated method looks a bit something like this:

    def witness_publish_feed(self, steem_usd_price, witness_name, wif, sim_mode=True):
        op = Feed_publish(
            **{"publisher": witness_name,
               "exchange_rate": {
                   "base": "%s SBD" % steem_usd_price,
                   "quote": "1.000 STEEM"
               }}
        )
        tx = self.steem.constructTx(op, wif)
        if sim_mode:
            return tx
        return self.steem.broadcast(tx)

I have some other witness related goodies in works as well...