It’s not as bad as it sounds, though.
Once the Nintendo Switch firmware update 6.00 hits, you will not be able to unlink your Nintendo Switch Online account from your local profile, Nintendo has confirmed. Now before you panic, read what this means below.
This does not mean you can’t deactivate your profile on your Switch to use it on another one- you still can. That hasn’t changed. This doesn’t mean you can’t change the region for your Nintendo account. You still can, and that hasn’t changed. All this means is that when you link your Nintendo Online account to a local Switch profile, you can no longer unlink it. This is being done to prevent save file duplication and scumming, and is in fact identical to how other consoles, such as the PS4 handle it.
But yes- if you would rather have your online account linked to a different local Switch profile, you should do it now, ahead of the Switch Online service launch next week.