Technology

You’re right that a lot of Terms of Service documents and similar agreement documents have language that reserves the right to modify those terms.

At the same time just because something is in the terms doesn’t mean it can stand the test of adjudication and terms as well as changes are often challenged in court with success.

Unity is in a particular tricky situation because the clause that governed modifications in their last ToS explicitly gives the user the option to pass on modifications that adversely affects them and stick with the old terms:

Unity may update these Unity Software Additional Terms at any time for any reason and without notice (the “Updated Terms”) and those Updated Terms will apply to the most recent current-year version of the Unity Software, provided that, if the Updated Terms adversely impact your rights, you may elect to continue to use any current-year versions of the Unity Software (e.g., 2018.x and 2018.y and any Long Term Supported (LTS) versions for that current-year release) according to the terms that applied just prior to the Updated Terms (the “Prior Terms”). The Updated Terms will then not apply to your use of those current-year versions unless and until you update to a subsequent year version of the Unity Software (e.g. from 2019.4 to 2020.1). If material modifications are made to these Terms, Unity will endeavor to notify you of the modification. If a modification is required to comply with applicable law, the modification will apply notwithstanding this section. Except as explicitly set forth in this paragraph, your use of any new version or release of the Unity Software will be subject to the Updated Terms applicable to that release or version. You understand that it is your responsibility to maintain complete records establishing your entitlement to Prior Terms.

https://web.archive.org/web/20201111183311/https://github.com/Unity-Technologies/TermsOfService/blob/master/Unity%20Software%20Additional%20Terms.md

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.

I pose you this, I open a book store. I say my terms of service is say, all non racist books are allowed to sit on the shelves. I then later say, "I now own the copywrite and that physical copy of any book placed on my shelves. The new ones, the existing ones, and the future ones." You'd be scrambling to get my books back before I pretend a contract you never agreed to is on effect and illegally steal them.

I dont know if thats true. however, somtimes for whatever reason it goes out of your control and you cant revoke access to the game binarys (foss, public domain, pirated, etc...). Unity still wants someone to pay.