If you move to Drupal 8 from Drupal 6/7, you'll be using the new core migration system.

Migrate team lead benjy has just posted a plan to finalize the migration system, a "meta" issue which outlines what work's already been completed, what's left to be done, what's blocking what, and how to get involved.

Migrations are an extremely high-impact place to throw time and energy, so if fixing Drupal 8 release blockers isn't your thing, but being able to actually move to Drupal 8 when it's ready is, please jump in and lend a hand! :D