Hi,
it would be great if we could decide soon when our next few major
releases will happen. This will allow:
 - release managers to start allocating their shifts for early 2020;
 - developers to organize their work; this particularly matters for
   sponsor deliverables with deadlines.
The starting point is the release schedule that we inherit from
Mozilla: 
https://tails.boum.org/contribute/calendar/
Here's an initial proposal, optimized towards minimizing the number of
major releases we have to do, while meeting our sponsor deadlines.
My goal here is that we identify bugs in this draft:
 - 2019-10-22: Release 4.0 (major release)
 - 2019-12-03: Release 4.1 (bugfix release)
 - 2020-01-07: Release 4.2 (bugfix release, with one exception)
   Tails Upgrader MUST support Endless automatic upgrades (#15281); if
   it's not ready in time, instead ship that in a beta by the end of
   January; and then some minor adjustments are needed below.
   Automatic upgrade from 4.0 and 4.1, using the old upgrade system.
 - 2020-02-11: Release 4.3 (bugfix release)
   Automatic upgrade from 4.2, using the new upgrade system (but still
   with aufs-based diff).
   From now on, users of Tails << 4.2 must first automatically upgrade
   to 4.2, before they can automatically upgrade to the current 4.x.
   Alternatively, they can do a manual upgrade. UX will tell RMs which
   of these options we should advertise.
 - 2020-03-10: Release 4.4 (bugfix release)
   Automatic upgrade from 4.2 and newer (still with aufs-based diff).
 - 2020-03-21: potential emergency release that traditionally follows pwn2own
 - end of March 2020: Release 4.5~rc1
   MUST switch to overlayfs (#8415).
   If GRUB and Secure Boot are ready to ship as well: awesome!
   Otherwise, we'll need another major release by the end of July.
   Automatic upgrade from 4.2 and newer (now with overlayfs-based diff).
 - 2020-04-07: Release 4.5 (major release)
   Automatic upgrade from 4.2 and newer (with overlayfs-based diff).
Is there any issue with this tentative plan?
Other factors that we should take into account?
Thanks in advance!
Known issues:
 - I don't remember ever getting this right on first try :)
 - Mozilla may change their release schedule. This will cause less
   trouble than usual wrt. sponsor deadlines: MOSS folks will
   understand if we have to shift our releases accordingly
   and thus deliver something a little bit late.
 - I did not reason about the timing of the Tails Installer changes
   that the migration to GRUB will require. Worst case, we'll have to
   make another exception and ship them in a bugfix release.
Cheers,
-- 
intrigeri