It seems that the number of FS2004 add-on planes has been rather low compared to previous versions of FS
Yeah, there are a few types of aircraft that are poorly represented by the freeware community. I personally want an equivalent of FS2002's long range Falcon 50, although there appears to be a Citation X on the horizon.
Still, using resources from previous versions there have been plenty of excellent releases both commercially and for free, like the complex Piper Meridian and the pocket-rocket Legacy. I don't think the new SDK will add much to what most experienced add-on creators already know.
"Nothing livens up a robotic hymn of doom more than an amazing pair of jugs." - Brak