Creative has released an updated line of cards in the August-October time frame 8 years in a row. I think it is safe to say they will release an updated X-Fi line roughly a year from now. That wasn't really the point though.
The video card market is a pretty good guide to use. Whatever the new feature for that generation is (T&L, DX8,DX9, etc), the software rarely supports the features until the next revision of cards is released simply because it takes time for developers to implement the features. So the early adopters end up with cards that have features they don't get to use, while those that upgrade later get to use all the features out of the box and know which features are really worthwhile and which are worthless. One positive of going with X-Ram now as opposed to being an early adopter of video cards, is that with video cards, not only are the new features not supported, but by the time they are, the first generation of cards are often underpowered to take advantage of the new software. This should not be an issue with X-Fi, as Creative will not be updating the processor any time soon.
One thing Creative has going for it is that they are the only game in town. There is no competing standard to fragment the market. This is a good thing as far as developers are concerned, they only have to code for one standard and most of the market will be able to take advantage of it.