If I understand the goal correctly, it seems the best thing to do is to soften the wording shown to users when their question is closed due to being off-topic.

If I understand the goal correctly, it seems the best thing to do is to soften the wording shown to users when their question is closed due to being off-topic, and explain to those users what their alternative options are.

• "Content that does not belong on Stack Overflow": close, and delete if it's unsalvageable.
• "This isn't a question I am interested in": click away, add any uninteresting tags to your ignore list if they aren't there already, possibly edit the question to add those tags if they aren't already present.
• "This is high-quality content that it worth promoting": upvote, possibly use a bounty to reward an especially good answer.

If it is your allegation that the community is wrongly using the close/delete features on content simply because we aren't personally interested in it, then that allegation should be substantiated. The solution would be better education for appropriate use of these existing features, or perhaps revocation of privileges (e.g. temporary block to the site) for persistent abuse.

• "Content that does not belong on Stack Overflow": close, and delete if it's unsalvageable.
• "This isn't a question I am interested in": click away, add any uninteresting tags to your ignore list if they aren't there already, possibly edit the question to add those tags if they aren't already present.
• "This is high-quality content that is worth promoting": upvote, copy a short-link to share it off-site, possibly use a bounty to reward an especially good answer.

If it is your allegation that the community is wrongly using the close/delete features on content simply because we aren't personally interested in it, then that allegation should be substantiated. The solution would be better education for appropriate use of these existing features, or perhaps revocation of privileges (e.g. temporary block to the site) for persistent abuse.

Goal: We want to decouple quality signaling from the asker’s ability to receive an answer

This is a bad goal which will harm the quality of content on the site. If a question is too unclear, vague or open-ended in its current state by our standards, then there is a likelihood that any answers written will not address what the asker actually wants, and that subsequent edits to the question to make it clearer and more focused will obviate the already-written answers. That is why we prevent answers being written on questions while they are in such a state.

Goal: We recognize that well-formed, opinion-based questions have value, but we also know that not everyone cares for them. Our goal is to make this content opt-in/out based on individual preference.

This is not as bad as a goal, but it's still bad and will harm the quality of content on the site. In practice, it is much harder to set clear standards for which opinion-based questions are acceptable and which aren't, and this will lead to more low quality questions being written and not removed.

Moreover, the userbase who currently curate questions and answers are probably not much interested in curating opinion-based questions if there are standards which allow them, so having an opt-in/out section of the site where most curators don't go is a recipe for slop and spam.

Goal: We want to prevent the “hard lock” failure mode where questions are closed against a “duplicate” that may not actually solve the asker’s specific problem.

This is a bad goal because it is based on a false premise. Question closure is not a "hard lock" any more than any other closure reason. If a question is not really a duplicate, this can be resolved in comments or by editing the question, and then the question can be re-opened.

If you think it should be easier to get such questions reopened, that's fine, we can talk about that. Allowing duplicate questions to stay open for answers is not a suitable alternative, and will only result in the 99% of genuine duplicates receiving duplicative answers from rep-chasers.

Goal: Maintain Stack Overflow’s focus on programming without making “Off-Topic” feel like a shut door for users with legitimate technical questions that may belong elsewhere.

I must say I don't really understand what this goal is. If it's really just about making people feel better when their questions are closed as off-topic, I don't see how expanding the set of allowed topics (as your idea suggests) would do anything towards this goal. There will still be topics that aren't allowed, and questions on those topics will still be closed, and the people who wrote those questions will still feel bad about it.

If I understand the goal correctly, it seems the best thing to do is to soften the wording shown to users when their question is closed due to being off-topic.