The changes in Mavericks make it possible to connect a DisplayPort monitor to your MBA and also use an Apple TV as an external display - I've just confirmed it on my setup - but that is pretty slow over wifi.
The issues with connecting monitors to the MBA are in hardware, not software. For example, the reason why you cannot connect a DisplayPort adapter to the Apple Thunderbolt Display is because the monitor itself uses the DisplayPort channel:
Connecting two displays to the MBA requires two thunderbolt devices.
The first device can be either the Apple TB display or one of the Thunderbolt docks with a DVI / HDMI connector. Both of these options use the DisplayPort channel, so connecting a DisplayPort monitor to them won't work.
This is where the second Thunderbolt device comes in (a hard disk or other device with two TB ports for pass-through). This acts as a man-in-the-middle and can extract a second DisplayPort signal.
So your setup will look like this:
<Air> -- <TB dock/display> -- <TB drive> -- <DisplayPort monitor>