I posted my slides to twitter also, and got some very interesting suggestions from Vicky Steeves at NYU.
In brief, she mentioned that GitLab (a service like GitHub) has a built in continuous integration service that can use Docker. So that removes the need for travis-ci and circle-ci, that I described in my talk, potentially saving some time. Good examples here: https://gitlab.com/jangorecki/r.gitlab.ci & https://bertelsen.ca/example-gitlab-ci-yml-for-r-projects/
The GitLab services look good, and I plan to experiment with it, but the R community is mostly on GitHub, so I think I'll probably stay where the community is for the moment. Plus my travis-ci and circle-ci tooling is very efficient now, so I'm not sure that there's a lot of time to be saved by switching.