40,000 Mile Service today

A bit of feathering is normal particularly if the tread blocks are predominantly loaded in one direction, such as the rear tires which only do braking. I've been doing cross rotations ever since a tire dealer did one which fixed a pull to the side about 20 years ago. It turned out my alignment was good, but the crown in the road had caused the tires to wear slightly cone shaped.

I haven't actually cross rotated the tires on my Prius yet, as I'm still under 'yota-care for another 6 months and am just happy when the dealer remembers to reset the service reminder, which they're batting 66% at currently.