I see the lesson on "extraterritoriality versus exterritoriality" somewhat carried on.
I'm not sure what "megacorporate status" is supposed to mean regarding "the process for multinational corporations to qualify for exterritorial or even megacorporate status".
Most author simply used the term "megacorporation" to means "big corporation." The only times where it seemed the word was somewhat defined, in Corporate Download and Corporate Guide, megacorporations were the AA and AAA rated corporations (it's the definition that was used in Shadows of Europe and Shadows of Asia). Which meant exterritorial status is part of the megacorporate status. It's a package, and you couldn't qualify for exterritoriality without qualifying for the rest (issue of corporate citizenship and currency).
From a metagame point of view, I'm dubious at the intent. I don't think this is something happening because that's a story some freelancer absolutely wanted to tell for a long time. The purpose is more likely to be to reduce the numbers of AA-rated corporations. But what's the line of reasoning?
Did someone said "Oh, there are too many AA corporations, we're not able to keep track of them all and provide plots for each of them. Let's get rid of a few." ? The line barely manage to have one or two ongoing plots for the existing AAA corporations, great dragons, not to mention countries or AAA's subsidiaries.
Corporate exterritoriality is important in Shadowrun, story-wise. The facilities were cops cannot enter and corporate rule is the law are a major plot device that gamemasters use. When there is sixty or so exterritorial corporations, a gamemaster can find one that suits it needs for the story he wants to tell, one that is inconspicuous enough, or even add one to the list without anyone bothering. Where are we heading at? "If you wants to have an exterritorial building in your story, you MUST use of of these twenty-five corporations we put on the list."