Posted by chx on September 30, 2011 at 4:20am
On November 1, 2011, all Drupal 8.x core files will be moved into a /core folder. This will break nearly every patch in the 8.x queue, requiring them at least to be re-rolled against the updated directory structure.
After that date, backporting 8.x patches to 7.x will no longer be trivial.