Add option for sound (i.e. speakers) on device
Hitomi offers some personal / grandparent feedback: She wishes that it had sound. I explained your reasoning, which I tend to agree with. Her reply was that it gets easy over time to ignore something silently playing; but if she heard Sayuri's voice from the other room, she'd be drawn in to look and constantly re-engaged. I can imagine some interesting demographic and use case clustering:
a) people who are used to having a TV on vs. not will respond differently. I am a "not" person and I believe you are too, so we may be more sensitive to "junk noise". Many households are quite different.
b) How much time is spent in the room where the frame is vs. nearby. Right now it's in the center of our main space, so of course we notice it often. Hitomi would have it in one of 3 or 4 main spaces in her house, since she and Alan have their own "corners" of the house to do stuff, and drawing her across from another room might be important.
c) How long people have had the device. Aside from yourself, all your data points are "weeks" at present -- I will be really curious how people's attention evolves. You might consider building in some sort of cheap proximity sensor (possibly just "rapid change in brightness" from a 10-cent photo resistor) that you can build some very simple algorithm from, so you can judge how often people come over and watch, and how long they stay. You'd probably need to disclose that; it could be a great item to add as a sub-category on the Kickstarter campaign, and offer a discount plus some "insider club" status for giving you that product feedback data.