My two penneth:
As far as I'm concerned, 29ers are just another design avenue to be explored. Once a general direction of their development is established (if it's not already), then their strengths and weaknesses when compared to the established 26" bikes will be understood. It is then up to the user (us) to choose the bike that suits what we want to do with it.
As for the competition side, the rule-makers will most probably restrict their use/modify the courses if they start to become the only way to be competitive. If you want to dent the competitiveness of a 29er, just put a few tight switchbacks in the course. Engineers will always find a way of improving something if they are presented with a problem.
2011 Orange 5 - n/a
2013 Boardman Hybrid Comp
2015 Trek Fuel EX 7 27.5
Rich, you beat me to it
One day your life will flash before your eyes.
Make sure it's worth watching!!