OP_RETURN and 40 vs 80 bytes: If the miners agree with you, you don't have to care what the network relays. Has Counterparty directly approached miners, to get them to mine 80-byte OP_RETURN transactions? What was the response? If the miners agree, great, let's do it. If the miners don't agree, there is no point supporting it in Bitcoin Core software.
As a miner I fully support exploring any functionality which adds value to Bitcoin, the only request being that introducing it be done in a controlled manner. The risk of increasing OP_RETURN to 80 bytes does not seem to outweigh the potential benefits, especially when multisig might not be prunable.
Of course a lone miner's opinion is unlikely to sway the argument, so what would the dev criteria be -- a major pool supporting the change, Gigavps getting onboard, a certain number of signatures obtained for a petition, etc?
I'm talking about miners -- the people who collect transactions into a block -- not the people who contribute computing services to a mining pool, yet have zero impact over how the network is run.