You know, I remember reading that part of the letter column and just thinking that it'd be one small article a year. Looking back at it, it makes much more sense that they mean it as an annual monthly theme for the magazine. This is great news! Booyeah!
While I have campaigns that I like more than others, I'll be happy with, quite frankly, anything we get, so long as it's done well (e.g. doesn't feel the need to alter the setting in tone).
Paizo people, two words for this annual theme: WEB ENHANCEMENTS! You're going to have more material than you know what to do with (the previous editor of Dragon said so himself in the #315 editorial), and likewise, the readership will be screaming for more than you can possibly deliver in one issue. Add into that that web enhancements of this sort will probably lure more people into buying the issue, and that they don't have space limitations, and how can you go wrong? Please think seriously about web enhancing the campaign classics!