This discussion fits more with https://discourse.julialang.org/t/0-6-nightlies than with this topic, it may be worth splitting the thread.
Since people appear to be using the release branches for day-to-day-work (the readme recommends it, which maybe we should change), I’ve gotten more cautious over time about merging things to release branches that haven’t been fully regression tested against packages and the benchmark suite. So I tend to do backports in large batches right before a release - people are welcome, encouraged even, to help out with testing while those are under preparation, and I do trigger binary builds of those branches for testing purposes. Watch the PR’s and set an email notification filter for “[release-0.*]” or “backports for” if you want to be notified of those while they’re in progress.
We have more pressing things to deal with when it comes to buildbot configuration, like rearchitecting all of them, to worry about adding nightly builds off of a branch that currently isn’t configured to do so. There is a new @jlbuild functionality that’s being worked on where people with commit access can more easily trigger buildbot jobs for given commits, branches, or pull requests. A nightly comment on the latest state of the release branch could accomplish what you’re asking for, but you won’t get much of anything different from the latest release until the next fully-tested batch of backports are being prepared.