Per https://groups.drupal.org/node/305573 Drupal 7 issues are no longer counted against thresholds.
However releasing Drupal 8 requires a working upgrade path from Drupal 7, and for the 250,000+ sites still running Drupal 6, they need to be able to upgrade to Drupal 7 first (unless they use migrate in contrib, but we didn't do that in core so it doesn't help with the core upgrade path).
This means there needs to be a working upgrade path with no data loss from Drupal 6 to Drupal 7 before 8.0 comes out.
Unfortunately this isn't the case at the moment, so opening an 8.x issue to track this.
https://drupal.org/project/issues/search/drupal?text=&assigned=&submitte...