I am using an Asus RT-AC66UI ad my main router, running AdvancedTomato which have very decent traffic monitoring utility that displays interactive graphs for real time IP traffic (LAN side IPs), plus historical data. It's kind of useful for people who have limited monthly bandwidth (welcome to my world), so it's kind of useful to see what devices are consuming bandwidth.
I have gone through the documentations for OpenWrt regarding bandwidth monitoring and checked the different packages. It doesn't look like there is one package that can do the same easily. There are packages that show per IP traffic and there are packages that show historical, but I didn't find a package that does both, plus the interface and graphics is really outdated.
I love that the OpenWrt is continuously updated and maintained, thanks to the community here. I believe the development of such package could really be a good add-on to a great project. I'm not technically able to develop such tool, but I could provide screen shots of AdvancedTomato interface as starting point