OTA Delta upgrades
@rhunault : Applying OTA upgrade don't work (fail preparation step from within LineageOS) when phone got rooted and busybox is installed. Consequentially, users customizations of the system, unrelated to system upgrades, are wiped out like if a new rom was installed at each OTA upgrades, requiring the user to reapply busybox and rooting zip files manually, which is undesirable.
When applying OTA delta upgrades from Cyanogen/LineageOS, that behavior doesn't show, since the preparation phase doesn't try to create the differential file, which is created and downloaded from OTA server to deploy deltas itself.
As a result, this would mean less storage space needed from e.foundation to store system images, but more CPU time and IO in creating those delta OTA images on server prior to permit distribution of them.
That would mean changing the client to permit differential OTA downloads between two versions. That would also mean changing the OTA server to host delta OTA, and maybe only monthly or bi-montly full images.