It's all coming together. The current wireless driver isn't Quantenna's performance driver yet. MU-MIMO for instance isn't enabled yet.
FW development is still very active. Look at the current firmware as a pre-release of sort - Asus intends to have a firmware based on the new Broadcom SDK7 environment in the future, which will bring (amongst other things) very notable improvements with USB performance.
Keep in mind that the router is currently still kinda in its pre-release stage. Wider availability is only planned for the end of August.