"limited" in this case means (using b43, as there are no alternatives for the BCM4360 chipset):
- limited to 54 MBit/s
- no HT rates supported
- no 802.11n (aka greenfield mode)
- no 802.11ac
- not very reliable or stable operations
I can't imagine any use case involving wlan operations where the Asus RT-AC68U could be under consideration for running OpenWrt - and no, this situation is extremely unlikely to change in the future.