A decision was made in the architecture meeting on October 31, 2013 with at least Philipp, Jan and Daniel present that same name siblings in JCR will officially not be supported in Magnolia. As i understand it, in many ways same name siblings are already not supported in many specific cases. And now we can simplify the system by enforcing this policy.
(Note that this was raised by http://jira.magnolia-cms.com/browse/MAGNOLIA-5311 and its related support ticket.)

Tasks:

• change the default node type definition to not allow same name siblings in a first place and
• distribute script to update existing installations with new node type definition
• add install condition to check that same name siblings are not allowed

Also, it was decided that changing the nodetype will only be done in 5 series. For 4 series we have the fix in the linked ticket: http://jira.magnolia-cms.com/browse/MAGNOLIA-5311