I don't think you need to worry about it too much. It's only being used for eye candy now, and no major programs made today make much use of it. If you buy a mid-range laptop, you're always going to expect that in a couple years it will struggle with high-end software, and waiting for a new iBook only means you'll start your two year wait a little later.
Your iBook will run all of today's programs and most of tomorrow's programs for the next 4 or 5 years. If you want one now, I'd suggest not putting it off. What happens in two months if there's no upgrade? That's two months you didn't get to enjoy an iBook.