I'm not so sure. Although the opportunity hasn't really even come up, one thing that Reddit has never done is make an agreement along the lines of, "You can use X version of this software under this license forever," in their own ToS, and then suddenly go back on it and declare that, actually, everyone they had that agreement with is now subject to arbitrary new rules. While Reddit has done some sketchy and user-hostile things in the past, it's an entirely different category.
It's a can of worms that cannot be closed. Even the apology-promises they're making right now are subject to random change, because they've made clear that they don't see their own ToS as binding for them. The article says, "We will make sure that you can stay on the terms applicable for the version of Unity editor you are using – as long as you keep using that version," and we're supposed to be reassured by that, but they've already said that exact thing before and shown that it was meaningless. What's to stop them from deciding next week that they changed their minds on their commitments again? They may have learned that they can't make such grand changes all at once without a boycott, but they could think that they can still roll out the same types of changes piecemeal over the next few years (and they might be right). What's to stop them from finding new ways to skirt around these commitments in the future (for example: adding some sort of planned obsolescence to future LTS versions to ensure that, even though you are technically allowed to use them under an old ToS, actually doing so would be completely untenable)?
Personally, I wouldn't trust anything this company says unless I have a legally binding contract with them, with clear damages defined if they break it (this may be the case for some larger studios, and that's fine for them). They can say anything they want in a PR release.