I haven't heard anything on the subject, but Nintendo's eight-character limit is more widespread than just Animal Crossing. Is there still an eight-character limit for file names in other Switch games like Breath of the Wild?
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I honestly hadn't noticed that this was a widespread Nintendo thing, so I don't know. Maybe? (Though, for Breath of the Wild I'm pretty sure that you have to play with "Link" because of voice acting, though granted it's been a while since I've played).
I haven't seen or heard anything about the character-limit being changed, so my assumption for now is that it won't change - they've had plenty of opportunities to do so in previous installments but never have, after all. (I came to that conclusion upon New Leaf's release, so I've already accounted for it with the name that I've chosen for my ACNH island.)
As 707penguin says, it has long been a standardised thing with Nintendo, for whatever reason. It was born out of earlier limitations, but it's stuck around far beyond them.