From the Bleeding Cool report on DC's panel at Megacon:
I find the part I bolded really encouraging, actually. It demonstrates that they're aware that much of what makes Wally popular is his history and his growth, and they want to leave that intact. They haven't found a way to solve that problem yet (or if they have, they're not saying), but it sounds like whenever Wally returns, it will likely be in a form that most of his fans will appreciate.That led us to a young man that asked about Wally West, to which of course I clapped and seconded. Dan and Eddie gave an answer that is going to keep me at bay with nerd rage for a while longer. He said because there were de-aging Barry, they didnt want him to be the same age as Wally. Plus they didnt want to take away Wally’s kids and family or make him a teenager again, especially with Bart already in that role. Dan also pointed out that someone close to him is a big Donna Troy fan, and Donna was given the same treatment when Wonder Woman was made younger in the relaunch. Their answer was that they are simply focusing on establishing the characters they started out with in this new 52, but not saying those other characters don’t exist or aren’t around in some way. They understand that everyone’s character is someone’s favorite. They just ask us Wally and Donna fans to be a bit more patient with them and those characters will be seen once more.
As for the difference between the treatment of Batman and Flash, I think it's safe to say that Batman can share the spotlight with so many Robins because he commands a much, much bigger spotlight. If the Flash is seen to be able to support more than one book a month, you can bet DC will look to capitalize on it with spinoffs. And that would be strong financial motivation to reintroduce Wally.