MapReduce is being deprecated in 6.6.0, and a note needs to be included in both the Release Notes and the Developer Guide.
This deprecation note has been added and published; a link to the published document on the customer portal is below: https://access.redhat.com/documentation/en-US/Red_Hat_JBoss_Data_Grid/6.6/html-single/Developer_Guide/index.html#chap-MapReduce