I just went to build a new image for my OPi3 and found that the 'Buster' option has appeared - I just had to go for it!
Everything seemed to have built OK and once I'd applied the WiFi 'fix' from here I was up and running.
The issue I've found is that I was unable to ping anything :
george@orangepi3:~$ ping 127.0.0.1
ping: socket: Operation not permitted
This seems to be because the ping binary apparently should have the SUID bit set, so :
george@orangepi3:~$ which ping
/bin/ping
george@orangepi3:~$ ls -l /bin/ping
-rwxr-xr-x 1 root root 73280 Aug 3 2018 /bin/ping
george@orangepi3:~$ sudo chmod +s /bin/ping
george@orangepi3:~$ ping 127.0.0.1
PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.118 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.127 ms
^C
I don't know if this is an issue with the Armbian build process or perhaps it is being echoed from the Debian Buster sources, and so I'm not sure how/where is the correct place to report it