Yeah I see this now (that it can't be hacked) my bad. I mean, I was under the assumption that the Switch itself was locked out of Nintendo Online by being hacked but if it isn't you absolutely have all the reasons to call Nintendo and get it unlocked through their customer service.
The only reason why you wouldn't want to call Nintendo is IF the Switch itself is banned, if it isn't, Nintendo always had an upstanding customer service. Be honest with them, tell them you purchased the Switch from a friend that got it locked through Parental Control from their kid, and that you bought it off of him and that they didn't know you could have the lock removed from Nintendo.
You'd like to use the Switch to go online, buy games and just enjoy the device that is essentially like dead paperweight right now and I am certain that after verification of you being an adult, they'll give you the code to unlock it. From there, you wipe it to a brand new Switch and you're set.
There is always the "Waiting for a modchip" solution but as someone pointed out, there is no specific date on when/how.