Use delta apk updates.

version1.apk >> version2.apk
version1.apk + diff file == version2.apk

When Updating app from version1 to version2, Play store downloads a diff file and combines it with version1 to create version2 of apk and then install it. The diff file is generated by google using binary differential algorithm, GDIFF. The size of the diff file between near versions is considerably lower than the final version apk.

Can fdroid use such delta updates?