As ressources are always limited and other requirements (e.g. Apple, Google, laws,..) can take additonal ressources , the devs never published any timeline.
They make reasonable work packages to avoid double work. When you check the changelogs, you will see that even the new versions are not announced and it can be any day of the week, just when it is ready.
I prefer this way, as it avoids discussions and dissappointments.