Strongly encourage people who submit things to include image descriptions / audio transcripts? Strongly encourage people to volunteer to describe / transcribe stuff for people who are not able to describe / transcribe their own content? Probably want to set two deadlines in advance, one for the first lot, one for the second, so that anything submitted by the first deadline will be fully accessible by the second deadline, with a big enough gap between the deadlines so that the people handling accessibility for the stuff submitted inaccessibly have enough time to do the thing?

Seek out volunteers (podficcing/podcasting experience probably preferable for audio quality reasons) to record audio description tracks for videos? Seek out volunteers to transcribe recordings of panels and Q&As and whatever and then record all those things for transcription?