They just need the right people, with Walmart's resources and name it won't take them a while to overtake Amazon.
supply chain disruption, disintermediation, 3D printing and all that. http://creo.ptc.com/2013/03/25/demands-for-increased-product-customization-on-the-rise/
It is not always possible to quickly find the right people who have a positive effect on the problems solution. But I don't deny that maybe this year Walmart will be able to do something in a similar vein.
I think that Amazon even in a few years won't cease its rise in value. Their good results will be due to the growing cloud business, an increased number of sales, the development of areas which heighten customers' interest. And this list of results is likely not limited.