I don't see it happening. As far as I can see, we have, for all practical purposes 7 slots filled up already, in the follow order of confidence. These folks are already well on their way or are most definitely going to be well on their way after a good showing at the USO and a masters tournament or two. Barring injury and major fallout from their consistent performances, these 7 are a shoe in to the WTF's, leaving really only 1 spot open, which Del Potro is soon looking to be the hot favorite for. We might be seeing more depth and challenge from the second tier of players like Wawrinka, Gasquet, Cilic, Haas and now Janowicz and such but overall the consistency of the 8 folks listed below almost surely pave their way to the WTF, so no real room for anyone new unless they're on the cusp and can upset the race towards the end of the year.
Which is more likely to happen: Janowicz qualifying for WTF or Federer NOT qualifying for WTF.