In terms of hardware changes, the only really impactful change would be in the inclusion of the second circle pad and a longer battery life. While the second circle pad isn't a deal breaker, the 4 hour battery life might be for some people depending on their travel times.
I don't expect we'll see a redesign any time soon.
The slow inital pace of the 3DS, which has since been more than corrected, hurt Nintendo's stock options and the company is still making recovery steps. A new piece of hardware, specifically one that replaces both the 3DS and it's addon, would splinter the 3DS install base too soon into it's lifetime.
In order to make the 3DS more appealing to developers and customers, the circle pad pro was made. I have one, and generally speaking it's actually a solid piece of hardware. However, the deal breaker is that it renders the device useless for mobile gaming in situations where you don't have access to a bag or suitcase - it's too big to fit in your pocket now.
I'd honestly get one now, and grab the pas pro if you need it. Your safe at least until the end of the year.
