RT-AC86U: Especially 2018 versions may be troublesome, 2.4G issues seems to be introduced in 2018 while early 2017 and latest 2019 are ok. In my opinion if you think about buy an 86U you should take a new one manufatured 2019 (or later 
).
Hanging after reboot is a known problem for all 86U, some have it more often than others with no reason. Latest firmwares could help but still seen in some case.
Thats why it would be helpful if someone brave with an 86U and more often seen it to test if GT-AC2900 firmware on it would solve it – then we would know it could be solved with firmware if Asus is willing to fix or that it is a hardware design failure.
DSL-AC68U: Good to hear that it can be reused as Aimesh node now with offical firmware!
Is it only enhanced to support Wireless backhaul or can it be used with LAN-backhaul too???
Have you tested both?
What I can remember they only did wifi-backhaul still missing wired.
You need to login in order to vote