In the interest of reporting back: this talk went really well. During the 45 minute session, I introduced AppImage, discussed why it should be used, and how they are created. I created an AppImage in a Centos 6 virtual machine, and then demonstrated that it worked on my Slackware host laptop. Then I put the AppImage on a thumbdrive and passed it around to audience members, one using Fedora and the other using Ubuntu, and they each confirmed that it worked as expected.
Next time, maybe a longer session, to discuss all the many features of AppImage, or maybe just a Birds of a Feather session at a conference, to find out how people are using AppImages, or to demonstrate how AppImages might be used.