Even on my Nexus 7 2013 I've changed the nav bar to rearrange the back button to the right and the multitasking button to the left.
Makes so so much sense this way.
Why?
Pretty simple: the back button is probably the most used one and it needs to be as near of your finger as possible.
Having it on the left is so annoying and uncomfortable. It's not as easy to reach as on the right.
Google should rethink this. Don't know why the did it like that on first place
I hope someday they'll change it. If not, Gravity Box is the solution.
One of the reasons I didn't go for the M8 was because the back button is on the left and I didn't want to root the device right away to lose warranty.
On the LG G2 and G3 you can rearrange the nav bar to your liking. LG has done a GREAT job here and therefore I'll always consider their devices just because of this alone.
On the Nexus 5 I could also change it with Gravity Box, and there you didn't lose warranty after rooting.
I chose the SGS5 also because of this.