The day was coming and it finally happened. A 29"er has won a major elite men's XC race. You can check out the report here. This won't be the last time this happens either.
The thing about 29"ers and elite XC racers is really all down to one little objection: Wheel weight. You will notice that the majority of elite racers that do use 29"ers, (admittedly, most are Subaru/Gary Fisher riders) use sub 2 inch wide rubber to help keep the rotational weight to a minimum. Of course, the wheels themselves are also very light weight works of art in them selves. Ryan Trebon's race winning set weighed 1350 grams complete with tubeless tape and valves.
This is just the beginning, as I said, though. There are newer developments on the cusp of being used in racing that will transform the 29"er from the odd ball choice in elite XC to a commonly seen sight underneath the fastest pros. Some of these new developments are radical.
Things like tubular mountain bike tires and wheels will become much more common place, and are being used now. For 29"ers, this will help relieve the rim from some of its weight. Another development that will change both 26"er and 29"er racing is the carbon fiber rim. It's been coming, and even I have laced up a couple examples in the past. The new versions will be very light, but extremely strong and will overtake the ranks of pro XC racing in a hurry once they become available. Especially when the carbon fiber tubular mountain bike rims I saw become available.
All of these things will affect choices made by the pros. No longer will wheel weight become the deciding factor against using a 29"er in competition. Courses will dictate what gets used and every pro will start to demand that their sponsors have a race level 29"er in the stable for their use. Not right away, mind you. This is an Olympic year, and many riders will be loathe to switch up components or wheel sizes before such an important event. However: that said, it wouldn't surprise me one bit to see one of the pros pull a 29"er out and use it come race day at the Olympics. After the Olympics is when I expect we'll really notice some equipment choice changes.