Maybe I'm shooting for the moon, but I'd like soft delete to be some kind of built-in database feature. It would be nice to enable it on a table then choose some built-in strategies on how it's handled.

Soft-delete is a common enough ask that it's probably worth putting the best CS/database minds to developing some OOTB feature.

Many data warehousing paradigms (e.g. Iceberg, Delta Lake, BigQuery) offer built-in "time travel," sometimes combined with scheduled table backups. That said, a lot of the teams I've worked with who want soft-delete also have other requirements that necessitate taking a custom approach (usually plain ol' SCD) instead of using the platform-native implementation.