I get that full transcriptions of video, sound, and image parts in a multimedia story for accessibility are not very practical, and it's not like I expect fanfic to go that far, but those letters are already text. And text that is an integral part of the narrative too. And it's just too small to read comfortably for me on a screen, especially with the typewriter effect, and I'm not even visually impaired or anything. Some stories displaying letters like that provide accessible alternatives, sheafrotherdon for example did in one of her Farm in Iowa stories, and I very much liked that, since I could take a look at the visual of the letter, then read the text in a comfortable font at a comfortable size.
With as much work as went into the presentation Missed the Saturday Dance, and I agree that it looks very nice indeed, how difficult could it have been to provide a link to a transcribed text of the all those letters as well, and make it possible for more people to enjoy it?