The timing is very confusing.
It can't be PS4 because Sony wouldn't take away hype from Feb 20th by showing what PS4 is capable of, announcing the platform branding, especially not with Bungie since their graphics track record isn't spectacular.
It could theoretically be Durango, which would be incredibly surprising because they would have to announce the platform brand and show its performance before or on the 17th, because again, they would not let Bungie to be the ones to reveal Durango. Pulling a massive surprise announcement would be unprecedented.
It's might be 360, but this would be pretty bad in terms of unveiling their huge franchise on old hardware with a team known for not amazing graphics on the platform.
So, if we can categorically rule out PS4, plot Durango in as an incredibly unlikely surprise and 360 as simply too stupid to happen, what are we left with for the 17th?
CGI, concept art, vidoc, story, setting, philosophy. In other words, we won't be seeing ingame gameplay footage on the 17th.