Is it possible to request it never be published, unless a trade goes sideways and its needed/one of the two/two+ parties requests it?
No, that would allow for loopholes like this:
if a potential scam victim receives the PM as BCC, I can't know everyone involved.
Is it possible to make this program entirely encrypted until the delay is up/ publishing requested ? (Not sure if this would even be possible).
Only if you send an encrypted PM, and publish the decryption later. But that defeats the purpose of using a third party to publish the evidence.
Ah I see. I guess Im forgetting youre working with what you can do here and now, which is limited since you arent the site admin (otherwise you could trigger the program to do stuff like disable BCC when utilized, of course right).
Is this the kind of thing SCs might be able to do one day, removing the need for a third party ? (Thinking of Satoshis 3rd party-less escrow SC proposal).