The way I read it is - "When we upgrade you, you'll still have ACCESS to premium connectivity, but you'll have to start paying $9.99 for it like all the new kids."
As in, you may already have premium, but when we upgrade you, you'll start paying for it.
And this makes sense, because the whole reason they provided free premium to MCU1 folks was that they couldn't access the high data usage features, like Theater. With MCU2 upgrade, you'll be able to access theater, and they'll want to charge you for the data use.
I could be wrong, but I'd think from Tesla's angle, it would be in their best interest to start charging folks. Hence why they even mentioned the cost in this article in the first place.