1: CLANNAD will come in fall 2007, and Haruhi will air in Spring of 2008.
Comments:Possible. After all, something that was given a preview is almost certain to come first. But you seem to have forgotten that CLANNAD is another of Key's "season" works, and is based around spring. If it airs in fall, it will end in either fall or winter. So far, the Key/Kyoani collaborations have aired in their own respective seasons.
2: CLANNAD will come in summer 2007, and Haruhi in fall, right on schedule.
Comments: Doubtful, if only that Kanon got 24 episodes and did well with them. AIR cut a lot of things out (although it was still really good), and though some people complained about Kanon's slowness, the majority of people appreciated it (myself included-- who says this blog isn't biased?). Considering Kyoani's policy of one show per season, Haruhi would have to be bumped back to winter.
3: CLANNAD will air in spring 2008, and Haruhi on schedule.
Comments: A few problems with this theory. For one, the TV network wouldn't have announced this series yet if it were airing over a year later. The other is that if Haruhi's coming earlier, why hasn't it been given the same announcement? Unless...
4: Haruhi is coming this year. However, its sudden lack of official information is a publicity stunt.
Comments: My favourite theory; it makes a lot of sense. Kyoani has had a lot of fun with this series and marketed specifically to those that have read the books. If you're not familiar with the next book, its title is Suzumiya Haruhi no Shoushitsu, and it revolves around Haruhi suddenly vanishing, with nobody but Kyon acknowledging that she ever existed. Don't you think that draws just a bit of parallel to this situation?
5: Haruhi is being delayed to allow more novels to be printed.
Comments: Also plausible. After all, we all hate when the show overtakes the source material -- it never ends well.
6: Our sources were wrong, there will be no second Haruhi.