We have milions of active users, and a large engineering organization, and our engineers push their own code. Every hour, every day. We've internalized writing

We have milions of active users, and a large engineering organization, and our engineers push their own code. Every hour, every day. We've internalized writing code that deploys well both going forwards and going back. 99% of all changes don't even need to worry about that, because they are UI/rules/bug changes, not base data schema. We actually don't roll back database schemata; schemata are applied before code that relies on the changes can be written, and thus must be backwards compatible! If you think you can't do it that way, think harder. It's not cheap to build all the necessary infrastructure and keep training all new engineers in the necessary skills, but it can absolutely be done and pay off handsomely. We never run stale code, and we never diverge far from master.