It's been a breathless past several weeks in Migrateland - with the core committers as a whole focused on trimming the criticals list for Drupal 8
to zero, Angie "webchick
" Byron has given quality time to help the Migrate team get unblocked, triggering a flurry of activity. All along I've meant to post a status update, but things have been moving so fast it's been "well, after this next commit..." Let's review where we stand at the moment, as of September 18, 2015.
From the initial decision to replace the traditional update-in-place (update.php) approach to major version upgrades with a migration-based (import into a fresh site) approach, it was made clear that the initial Drupal 8 release would not be blocked on the upgrade path. If the upgrade path was not "ready", Drupal 8.0.0 would release without it and be available for building new sites only. The plan was as Drupal 8 approached RC status the decision would be made over migration support in 8.0.0. That decision has been reached and published. By all means go ahead and read the official policy
as well, but tl;dr: the migrate API and the Drupal 6 upgrade path (and possibly the Drupal 7 upgrade path as well) should be part of the Drupal 8.0.0 release, but marked as "Experimental".