Thank you for telling me about it! My game is unlikely to reach 200,000 downloads so I'm not worried about it😀
While it might not sound like much the policy WILL be retroactive, so downloads from before the start date will be counted. Even unofficial/pirated copies. Given the time you've been working on this game it's unrealistic to expect an engine switch. I know some devs are switching to Godot. I don't know if it's similar enough to unity that you could take your skill with you but it may be worth changing over when ever you go back to your old games.
Having said all this with the backlash Unity have been getting even as a soulless corporation I can't imagine the current plan to remain in place. Time will tell Jan. 1st.
Dont make youreself small mofu. You have to consider that there are many people Downloading this game every time you put out an update. So that means you got you full download cout every two month or so or even something like every two weeks if we consider the hot fixes. The only way I could think of to reduce this would be to do lesser mini hotfixes and pack them together to do a patch once a month or so. Also the translations you could move the original dialogues to a Dropbox or a google doc for the translators so we don't hhave give you the translations like breadcrumbs and you put them out as soon as you receive them. But that are just ideas.