From 1511 release onwards it is possible to include extended node in the Datasource as mentioned at: http://scn.sap.com/docs/DOC-68674 with Description “Node Extensions -Usage in Analytics”.
But, the extended node cannot be enhanced into the standard datasource, you could instead :
create new datasource on the Standard BusinessObject and
then join the custom datasource with the standard datasource.
Business objects supporting extension nodes: http://scn.sap.com/docs/DOC-68053
Analytics Common mistakes to avoid in SAP Cloud Applications Studio: http://scn.sap.com/community/business-bydesign/studio/blog/2016/02/16/analytics-in-sdk-common-mistakes-to-avoid