After years of giving people free rein to play online, Nintendo decided to get with the competition and monetize it on the Switch.
"Switch Online" has been a thing since September 18, heralding the aforementioned premium price for online play as well as a suite of NES games (with the potential for official modded ROM hacks, something Nintendo left out of the promotional materials before launch), cloud saves and other smaller extras. According to the Big N things have been going swimmingly even if the initiative itself has a long road of improvements ahead of it.
Based on a statement in their financial results briefing for the fiscal year ending in March 2019, they note that the launch went "according to expectations," and that "more than half of total subscribers" opted for the 12-month family or individual plans. They explain that this number is "more than anticipated."
It's a bit vague and raw numbers aren't given, but with the Switch base hitting 22.86 million this month worldwide there's a lot of potential to increase that extra revenue stream.
Financial Results Briefing [Nintendo]