There should be updated datasheets within the next couple of weeks, the RM update should happen by the end of Q1, not sure if you are asking anything on MQX or what you mean by old document release. I believe MQX's next release is very soon, but you could check/confirm on the MQX forum, it is not specific to Vybrid.
Sample code for the Tower board can be found on the Tower web page, but there is nothing DCU specific in the sample code bundle, may have to look at MQX or Timesys for DCU related code.
Not sure what you mean by JLink-Lite is needed for Tower board, the only tool chain FSL promotes for the Vybrid Tower is ARM's DS-5 suite, either with the CMSIS-DAP, via USB only connecton or with the DSTREAM ICE. Other tool vendors support Vybrid, such as Segger and IAR, amongst others, but for that you will have to talk with those companies direct.
Ross