Yes, this. There is absolutely no sign that this is meant to be a magic band replacement. Or that magic bands are going away. As many have said here and on similar threads, Disney has spent a staggering amount of money on the magic band system. They're not going to replace a thing that all of their resort guests have (magic bands) with a thing that only a certain percentage of guests have (smartphones that support the
MDE app). Are they going to require that guests have a smartphone to stay at their hotels, because they won't be able to get into their rooms without one? Pretty unlikely, I'd say.
As I've said before, I see a couple of reasons for this.
1) It's a backup for the (sometimes flaky) magic bands. We see plenty of reports of guests not being able to get into their rooms with their magic bands. This way they have a backup method to use when that happens, which takes some of the pressure off the resort staff. Having a backup also is a guest satisfaction feature. The guest who's stuck outside their room door at 10 PM with two wailing, overtired toddlers and a nonworking magic band can just pull out their phone and get into the room, without having to hike to the front desk.
2) It's something frequent travelers are used to using. Most of the major chains are adding this capability to their apps. I suspect the manufacturers of the door locks provide an API that made it easy to add this to the MDE app. And development groups love the low-hanging fruit - quick, easy projects that add functionality, might make the guests and staff happy, and don't cost a lot of money.