One solution for performance degradation with soft deletes is to partition the table by some field like `created` monthly. Queries will need to include `created` in the query is the main downside.
Depends on the workload. In the past, I've worked on several workflow-based systems that performed lots of OLTP operations to drive live workflows forward, but once a workflow was done the operational data became a lot less interesting. So there it made sense to (say) partition the operational data and table by month, and roll off partitions after 3-6 months.
