Hi Josh,
You are correct, at this time we do not support adding attachments as part of editing a survey from the Inbox (OS of device does not matter). While we are looking to support this in the future, there is not a set date as to when this will be. I have made note of your request in our internal repository, and I would encourage you to continue utilizing the "Sneak peek" section of our documentation and GeoNet for announcements related to support of this feature.
You may also want to reference the following GeoNet thread which offers a workflow utilizing repeats (related tables) to manage the addition of photos via the Inbox.
Regards,
Brandon