When I was working on open source at Google this was also something we had to be very careful with: you don't want to make promises you can't keep. But this wasn't as strict as what Apple does, and vague estimates were allowed.

For example, here's what Chrome does: https://chromiumdash.appspot.com/schedule. All the dates are tentative and sometimes slip, but an engineer can point people to it, say "fix X made the branch cutoff for release NNN", and you can get a pretty good prediction for when X will get to what sort of devices.