https://www.techradar.com/news/nintendo-switch-online-membership-can-be-bought-using-gold-points

It looks like Nintendo Switch Online membership can be bought using My Nintendo Gold Points. 

Reddit user Ice Blast noticed the detail while reading the Nintendo Switch Online Service FAQ. Under the question "Can I use My Nintendo Gold Points to purchase the Nintendo Switch Online membership?", it states: “Gold Points can be used when purchasing a membership in the Nintendo eShop. They cannot be used for auto-renewal.”