... acting as a guinea pig
Here's the challenge:
* try to install the official 5.3.8 firmware on your Paperwhite 2, according to the
official instructions.
* report back.
Your potential risk: Not much, really. Most probably, the Kindle won't even allow you to update (leaving the "Settings > Update Your Kindle" grayed out). If it does allow you to choose it, the update will either a) fail (likely), leaving you with the exact state that you were in before attempting this, or b) succeed (unlikely), leaving you with firmware 5.3.8.
Your potential gain: Not much,really. You'll be my superhero (and probably for a few other developer's corner regulars, too). And I promise to invite you for a fancy dinner if we ever meet in person. And if you actually did manage to downgrade to 5.3.8, we also go on a binge after dinner...
... and now for real: why? because even just trying to install that update will help us to better understand the new device and software ("us" = some folks in the developer's corner).
Volunteers? The first confirmed answer wins!