OpenWrt recommended builds for AC56U (use at your own risk):
OpenWrt latest builds - http://downloads.openwrt.org/
Buildbot - http://buildbot.openwrt.org:8010/one_line_per_build
=======2015 Builds=======
openwrt chaos calmer 15.05 - download factory/upgrade firmware | packages | changelog + announcement
- SquashFS Getting Major Performance Enhancements in Linux Kernel 3.14
- added initial support for ARM based BCM47xx and BCM53xx SoCs
- built image for AC56U
=======2016 Builds=======
openwrt chaos calmer 15.05.1 - download factory/upgrade firmware | packages | changelog + announcement
openwrt designated driver trunk 16.xx (no LuCI GUI) - download factory/upgrade firmware | packages | roadmap
=======2017 Builds=======
openwrt LEDE 17.01.5 - download factory/upgrade firmware | packages | changelog + announcement + release notes
OpenWrt Fork by LEDE project builds download release/snapshots/packages and changelog/commits for AC56U (HWNAT) - http://lists.infradead.org/pipermail/lede-dev/
=======2018 Builds=======
openwrt LEDE 18.06.0 - download factory/upgrade firmware | packages | changelog + announcement + release notes
=======Upcoming Changes and Features=======
OpenWrt Summit - http://openwrtsummit.org/ + https://forum.openwrt.org/viewtopic.php?id=66773
OpenWrt Summit 2016 Livestreams - https://www.youtube.com/playlist?list=PL3bvPCw5QCLJ0xR1oXui6M7QBh6UElgvn
=======Useful Links=======
AC56U Wiki - http://wiki.openwrt.org/toh/asus/rt-ac56u + Techdata + ASUS Wiki + AC68U
AC56U Support Page - https://forum.openwrt.org/viewtopic.php?id=45190 + bcm53xx
Broadcom bcm53xx SOC Wiki - http://wiki.openwrt.org/doc/hardware/soc/soc.broadcom.bcm53xx
bcm53xx commits - https://dev.openwrt.org/search?q=bcm53xx
openwrt-devel mail archives - https://lists.openwrt.org/pipermail/openwrt-devel/
Random MAC address assigned with every reboot fix.
Hardware NAT Acceleration
https://dev.openwrt.org/ticket/11779
http://wiki.openwrt.org/doc/hardware/switch#features
ctf.ko - http://wiki.openwrt.org/doc/hardware/soc/soc.broadcom.bcm47xx#ethernet
https://lists.openwrt.org/pipermail/openwrt-devel/2013-August/020962.html
https://lists.openwrt.org/pipermail/openwrt-devel/2013-August/021112.html
HW_NAT - http://forum.ixbt.com/topic.cgi?id=14:62648-78#2842
hw_nat - http://wive-ng.sourceforge.net/?WN-MT_MT7620N%2FH:Istoriya_izmeneniy
----------------------------
OpenWrt GitHub commits - https://github.com/openwrt-mirror/openwrt/commits/master
OpenWrt GitHub Packages commits - https://github.com/openwrt/packages/commits/master
OpenWrt Packges Repo - http://downloads.openwrt.org/snapshots/trunk/bcm53xx/generic/packages/
OPKG commands - http://wiki.openwrt.org/doc/techref/opkg