Your current firmwares are covered by BackDoorLock then.
And the PW1 update does introduce Bookerly IIRC.
But you can sideload Bookerly via the font hack if you need to.
There are various UI changes etc. in the updates, which you may or may not want -- notice the major version number changed.
But as far as Amazon pushing updates in general,
that is only because of the crypto enhancements.
Your reasons for avoiding the newer firmware are no more or less valid just because Amazon is pushing people to accept updates which include crypto changes.
...
Here are kaznelson's margin/font size mods:
https://www.mobileread.com/forums/sho...postcount=1431
As you see, he hasn't bundled a version for the 5.6.1.1 firmware.