There has never been a way to postpone expiration of travel funds. I think the expiration date is set when you purchase, and you are stuck with it.
But there's never been differential expiration. Before you could not change the date from which they calculate expiration. But you could definitely refare and make the funds transferrable, for example. So there was definitely precedent for changing a feature other than the "start date" of the funds (for lack of a better term).