Well, USF has opened three new rides over the past year (Jimmy Neutron, Shrek 4D and now Mummy). I'd be shocked if the next major attraction doesn't go into IOA.
But when?
Busch Gardens is getting a major coaster in 2005. Disney is adding its biggest coaster - ever - in late 2005, early 2006. IOA obviously needs to come up with some kind of response. Next year may be too early but I can definitely see something significant going into the park by 2006.
However, I wouldn't buy an annual pass just based on that. Do it because you know you will get good value out of it. At $159 that's $6-$7 a month, a huge bargain if you plan on being at the parks.