Opt-in should always be the default. You should never force your users to become active if they do not want something.
You do not get responsible users if you shove stuff down their throat because you can somehow spin the narrative into them wanting the stuff.
Instead you should focus on educating your users and explain them why they should update, why you added that new feature.
One could argue that you also should provide huge new features as plugins so that the user can decide to use it.
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