You are right in terms of in-development and future games. But unity is also trying to enforce these terms on already released games. This could potentially bring a challenge to their subscription model, which essentially states you must continue to pay as long as your game is available. I don't know much about the law, but I do know that there are legal limitations on how rented/subscribed products work. These limitations are to prevent straight up scams from stealing from you and making it technically legal with some fine print. Which isn't too far off from what unity is doing now.
This is comparable to you renting a drill from someone to make a table. You agree to the terms that you must continue to pay a subscription as long as the table exists. Then unity drill co. decides you must also pay a fee every time someone sits at the table. Even though the table is already made, and you already had an agreement to pay for the drill you had previously used. Your only alternative is to destroy the table.
Just because the terms said they could modify the deal doesn't mean they can force anything on you as if you had already agreed to it.
You can't set reminders if you never knew the interview existed. It's still their fault, but it's an easy mistake to make.