Can’t wait for Android O? Neither I can, but you can at least make use of one feature a little early if you’ve got a mostly stock Nougat phone. The guys at XDA found that navigation bar customization was present in Nougat, and you can even use it without root. One dev has already pushed an app called Custom Navigation Bar that can make the necessary modifications.
Do note, though, Custom Navigation Bar won’t work with most of the more heavy-handed manufacturer ROMs like TouchWiz. That might trim down interest for more than a few of you, but if you are running a Nexus, OnePlus, Xperia, or other device with a fairly light rom (even LineageOS) then you can give the app a go. While it might not require root, it isn’t “one-click” easy to get things working. You need to have a computer nearby with both ADB and USB drivers for your phone, a cable to connect it, and you need to be comfortable using a Bash terminal or CMD.
Custom Navigation Bar