I have to admit, I'd be interested. It'd not often you see point guards with his size and ability. Still, from a practical point of view, he doesn't fill a huge need. Rondo will be seeing at least 32-35 mpg this season, if not more. So, there won't be a huge need for him. Moreover, I'm not overly fond of the idea of both of them on the court at the same time, as neither of them shoots very well. Having a lineup of Rondo, Livingston, Pierce, Garnett, and Perkins at times wouldn't space the floor that well.
That said, whenever you have a shot at netting a quality point or a quality big, I guess you go for it.
Still, I don't see this happening.