This is the response i got today from ta. It makes sense:
In recent years, as each resort is refurbished, Disney has been trying to offer more flexible rooms that would allow them to have rooms that are both wheelchair accessible, and available to the general public. For example, they lowered the thresholds to enter all of the rooms at Pop Century so that a wheelchair could get through the door of any room. They did not put sides on any of the new beds so they are easier to get into. They have shower chairs and grab bars that they can add to a room on a moment’s notice if someone needs them rather than having them permanently installed in only a few rooms that are designated as wheelchair accessible. Making some of the rooms have a shower only (so no tub to step over)was one of these changes that allows Disney to be flexible and, hopefully, not run out of wheelchair accessible rooms. So they will go to guests who need a wheelchair accessible room first and then be assigned to anyone. I definitely have the request on your reservation though so hopefully Disney will be able to offer you one of those rooms. There are actually a bunch of them now.