This is a growing misconception. You can still unlink your Nintendo Account on firmware 6.0; the only thing that is actually different is that you cannot unlink it from your console. Rather you will have to call Nintendo to unlink it for you.
Regardless, a linked Nintendo Account has 0 bearing on whether or not you get banned or not as bans are typically applied to the console not the account. And when the console gets banned, you have to call Nintendo to unlink it anyways. The only reason I see for unlinking the Nintendo Account is if you have any purchases you wish to hold onto in the unfortunate event that your console gets banned.