I think IPB and VB have good reason to be scared, considering the flocking attention xenforo has gotten in such a very short period being live. I expect to see IPB and VB change to be more like xenforo as fast as possible, to keep hold of their customer base... but the problem with anything old, is that they simply won't have the underlying framework to compete that xenforo has, being so new.
The one discussion about the xenforo addon to run the addon section here already has so many possible uses, none of which is really in the marketplace by either VB or IPB, even though IPB have download addon, its not like what is coming here, which goes those few extra steps of being completely self supportive by each dev.
I can see the more importers done by XF and incorporated, the more will be converting over. Even Paul's VB4 converter... it brings over CMS, Blogs, Albums, everything, so you can hold the data in hidden forums until products are available... Xenforo would make me nervous being a competitor.