This is a topic that gets people going, for sure.
You've probably guessed that I am not a fan of "walking" reservations. It's not good for the overall program, and I fear that "walking" will beget even more "walking." I may start doing so just as a defensive move. We almost always stay in one-bedroom or larger units, so the need to do so may be less.
DVC should either normalize the practice, incorporate it into the rules, and put it on the website so all owners can truly know and avail themselves of the opportunity to do so or eliminate the practice. In the middle of these two opposing ends, some number of free reservation modifications are allowed, after which the owner is charged a fee for further modifications.
I prefer the last. Everyone would know the rules and have an even playing field, as was intended. Everyone would still have the opportunity to flexibly modify a reservation at no cost, and, lastly, the opportunity to walk would be preserved if an owner wants to pay for it.