The difference is that there's no reason to keep the expensive 4k account.

The Premium plan is 4k streaming, and up to 4 devices. But now they want to keep those two features bundled, while limiting your ability to stream to 4 devices (because now they'll all need to be in the same house). Sharing my account was my reason to suck that up and pay 20 bucks a month for 4k streaming.

Now only I can watch it, or in OP comment's case only his mom can watch it, so there's no reason to not just switch to the basic plan with 720p for 10 bucks a month. Point is, there will be cancellations, but also a ton of people halving their subscription cost. It's going to hurt Netflix on both ends.