I wonder if the average consumer, who buys a set for around the tree, will see batteries as a feature which adds value.
Think about it. What makes battery powered devices so nice? They're portable. I don't see portability being of any use when your oval of track is set up on the floor in the living room. What makes battery powered devices annoying? Somehow you always forget to charge them. So you would be adding the annoyance of batteries without the benefits.
Certainly, for people who are planning to build immense layouts, or who want to build outside, not needing to worry about wiring and conductivity would be a bonus. But those are not most people.
I could see battery power eventually coming in as the new standard at the high end of the market, especially among modelers, whose nostalgia is for real trains, not toy trains. They will not be disturbed by the fact that their childhood trains are useless on new layouts built for battery power, which will inevitably have two rail track. But I don't think battery power will take the starter set market by storm anytime soon, unless it gets to the point that robust batteries are less expensive for the manufacturer than the little wall wart transformers.