Unironically you can put "what are good demos for agentic workflows at Google I/O that would be received well by the general public" into Gemini's AI Mode and get better suggestions for use cases than what they're showing.
Welp. I bit the bullet. Copied your question, opened the Gemini app on my iPhone, and pasted it to the new 3.5 flash model. IMO, the answer unnecessarily long, the suggestions were on par with what was mentioned and presented during the part of the keynote that I watched. Also, the summary table didn’t render correctly in the app but does render on web.
My conclusion: maybe they did use Gemini to brainstorm.