if by "perform mac address filtering" you mean create a whitelist of mac address allowed to connect, then the answer remains NO and i really believe it will always be NO. This kind of feature is clearly made for SOHO setups, and while UniFi can be used on SOHO setups, it's commonly used in larger (sometimes HUGE) setups. While there's no problem at all on using UniFi for smaller setups (sometimes 1 single UAP), some features exclusively for these small setups may lack and may never be present on UniFi.
You can, of course, block devices (mac addresses), but cannot create whitelists. For blocking a device through the WebUI, you'll need to have connected to the network at least once. Using API calls, you can block a never-connected device.
I have developed several solutions which basically offer mac-based whitelisting, and the ability to block mac addresses whenever this becomes necessary. One particular application of this is a self-service portal where end-users can manage their "budget" for a number of devices with access to the wlan.
This works nicely with the guest policies in the UniFi controller, and integrates by means of the API.
