Software updates tend to take time, at least if you look at the historical average. A few OEMs have been pushing the envelope recently, though. For example, NVIDIA is saying that Android 5.0 will be on the Shield tablet this very month.
The news comes via an NVIDIA demo video of the new OS running on a Shield tablet. There's not much to see in the video—it's just Lollipop on a Shield with a new UI for the Shield Hub and Dabbler. However, the November release is mentioned several times, so they must be pretty confident.
It's also worth noting that the device in this demo is the LTE version, which you can identify by the signal bars in the top right. Updates for tablets with mobile data can sometimes take a little longer, but NVIDIA has been good about that so far. When Android 5.0 is ready, it will be pushed out via an OTA update.