Well this time around there are a bunch of LFS'ers in the Pro Series who I think will make the DWC.
Jesse Nieminen, Hugo Luis, Vincent Staal, Danny Engels and Marcio Campos. Then there are many iRacers who didn't race the first Pro Series, but probably will be in the DWC; and several are good enough IMO to challenge Greger with enough practice (don't forget practice is huge, Greger practices everyday with the focus on one event only), such as Jeffrey Rietveld, Klaus Kivekas, Max Dell'orco, Luca Masier, Aleksi Aloma and Matthias Egger.
I also hope to make the DWC myself. I'm glad I didn't this time around actually since I'm not comfortable in the Dallara, it's too unpredictable I find, and requires me to learn a new way of driving, limited by front end grip. I think if when we see someone challenge Greger this year, it will probably be either Luke Mclean (has much better race than qual pace), or Richard Towler.