The Memory of Light will be published on Jan 8th...as Brandon Sanderson and Tor announced on his blog a few weeks ago. Very excited about the finale, it's been a long time coming. I started reading WOT when I was 13 years old, and only the first three novels were released at that point!!
Also sometime afterwards the Wheel of Time: Encyclopaedia will be released. Harriet is overseeing this apparently with no release date yet...my guess if it does come out it won't be until late 2013 or 2014.
As for casting...I've no idea. This has always been a difficult thing for me to think about.