I'm not fishing for a definitive answer on whether it was or wasn't a trial balloon. I'm more thinking, what do we make of a situation where the media could be used as a trial balloon, or as a sort of preemptive reveal by people opposed to an attack. Actually, those would both be trial balloons in my mind. In one case, if it's really a test more than a confirmation, then the government wouldn't assume too much about which way people will react. It would merely release the information in a way that seemed of manageable risk, or perhaps 'barely enough detail' to get people talking about how they should react. In the other case, the parties behind the leak place their bets more that an important audience (is it "public opinion"?) would often oppose an attack too if the information were revealed just now.
Arguably Wikileaks did much the same thing(s) in some respects. They released a lot of information that either tests what people think of the management of American foreign policy, or (for certain points of view) draws out pronounced criticism of American policy or practices. So to create some new subquestions... Picking through some of the responses:
1) Is there really no "news" here? We have a report of a short Israeli timeline (whether specified by leadership or inferred by outside observers) and window of opportunity for Israeli or US attacks on Iran. By now, we also have an IAEA report indicting Iran for a weapons track, which means there is some claim to an ethical or legal case for an attack by rationale that Iran signed the NPT. Does the weight and timeliness of the information not change when it's said to be about increasingly current and actual events? Honestly, I'm kind of struggling to imagine what would be "news" if not.
2) If the situation were reversed, would you be more concerned about the employment of news sites to get the message to us? What if the paper argued that Iran, and not the US, will likely launch an attack within a year? Would you say that should have appeared in the newspaper? Would that seem more worthy of an editorial discussion about then what happens (in terms of military events), because the anticipated PR story calls for some physical Iranian provocation and not a "preemptive" Western attack? Should newspapers not foster public talk about what a military confrontation would be like until the confrontation is already a hard fact to be reported, in either case? Or, when should they start opening a forum where people may discuss such things?
3) I'm gathering so far that there doesn't seem to be much surprise here at the Guardian covering this as a matter of course. Yet we have some sources saying this was all a leak, and possibly a criminal leak according to current Israeli leadership, to begin with. Now, when Wikileaks was releasing even redacted information without a government's formal support -- and I haven't heard many claims that it was a US-backed conspiracy -- well then, it seems to me there was a lot more discomfort expressed here. Assuming that people are more comfortable with the Guardian releasing this than say Wikileaks or another designated "activist" organization, why are you more comfortable?
4) I'm feeling skeptical that most people would take time to judge a source based only on what it releases in any given document, or even through a long and systematic comparison to other sources available. I think it has something more to do with the reputation we build up in our minds about sources of given types. I keep thinking that if Wikileaks had produced much this same article, there would be a higher level of discomfort. Would you assume that even the Guardian, which may be a fairly good example of a relatively liberal (if still modestly mainstream) press agency, remains beholden to either 1) government manipulation or 2) some more broadly defined national interest in a way that Wikileaks never was? Also pick your country or region whose interests to be represented, as the Guardian is a British paper and if I'm not mistaken, also a private company with at least some transnational presence and not officially an arm of any government? Alternatively: Is there some other clear line between investigative journalism and activist releases of information that in itself would serve to make this mundane and innocuous?
5) Finally, however you answer those... What does your view of the sourcing suggest about our ability as a public (or publics if you see great differences depending where you live) to gather useful information and to join a debate about what American policy vis-a-vis Iran should be? For example, do you think we have any "good" sources to judge what's really happening such that we could have a public debate about it before the policy decisions have pretty much already been made and sold through whichever media they are sold through? Could some of the very information needed for an informed public debate be tantamount to exposing the public/state to harm, no matter who reports it? Are the media sources we use to become "informed" too easily manipulated by designating some info secret, and for that matter by designating certain matters as "off topic" (e.g. 'editorial' where only 'objective' is to be allowed)?