Drupal 7 has a much longer lifespan than the (already pushed back) official date, and Drupal 8 has an essentially infinite lifespan because it can update in-place to Drupal 9 easily and the same will be true of Drupal 10, 11, ∞. There's no reason to rush an upgrade— but there's no reason to wait either.
How to keep modules compatible with Drupal 8.7 and below while still using the new services.