Wow, nice.
But still, from a user perspective, I’d expect to be able to list the JDKs I want to support, and have them running (as they usually do). It’s very appealing to have such machinery work with minimal configuration.
I also teach CI and SE practices, multi-jdk builds are a nice way to show how things can stop working with upgrades (e.g. illegal reflection accesses with modules) or require backports to keep going, or even custom environment detection.
Having to setup Docker adds a layer of unwanted complexity, it’d be nice to be able to reliably use the wondrously simple configuration of the Travis documentation.