As long as we're all allowed to speculate, does Iran need specific expertise to help them get beyond the software viruses that have plagued their nuclear program? Or was there expertise on that plane that could help them with missile guidance systems?
The way I see it, there are three likely possibilities. There was something or someone on that plane that A.) at all costs, could not be allowed to land in Beijing or b.) that, at all costs, needed to be secured by Beijing. Less likely, though certainly equally worthy of consideration, is C.) a government or organization that needed to secure a Boeing 777 by theft in order to use it later to infiltrate someone's airspace, most likely US airspace, with some kind of a weapon, a weapon big and bad enough to justify a conspiracy of this magnitude.
And I for one am going to applaud wild speculation. This whole situation is way out of the ordinary, and using it as an opportunity to explore what is and is not possible is healthy brainstorming.