QOS, and multicast are said to be next that only leaves BGP, IPv6 and Security. I remember Brian saying he did the BGP section, but didn't like the format and is starting from scratch. Personally I feel the V2 & 3 workbooks did a great job of covering the core of BGP. Beyond that I would go through the command reference and try out and the commands that couldn't be covered in the workbooks. The only comment I would have on improving the workbook would be that I have probably setup hundreds of neighbor relationships throughout, but was never forced to use any of the rarer commands like disable-connected-check or transport connection-mode.