Nintendo Switch Online has been available since September 2018. To date, it has registered at least 9.8 million subscribers; no mean feat given it has only been available for eight months.
The most interesting bit of all is that Nintendo Switch Online has considerably fewer bonuses for the players compared to when playing it on Xbox Live or PSN. Though there have been complaints about Nintendo choices of free games.
The publisher (Nintendo) has also released new games exclusive to Switch Online subscribers. The most recent being Tetris 99, which was given a free gift to anyone owning a Nintendo Switch Online. It is reported that the company has sold over 34.7 million units worldwide.