UPDATE: Nintendo has just fixed the typo indicating that the Nintendo Switch online paid service should still be launching in 2018.
When Nintendo announced the Nintendo Switch in January last year, they originally revealed that the paid online service would be coming late in 2017. This later slipped until 2018, but it might have now slipped until next year.
The latest article that Nintendo has published on their website about downloading the game digitally has a reference at the bottom of the page that the paid online service is now coming in 2019. This is set to include expanded online capabilities, discount as well as free NES games that have online functionality.