When there are big changes, I’ve seen a lot of sites, and even some applications, allow users to opt-in to the new version to try it out, or opt-out of the new

When there are big changes, I’ve seen a lot of sites, and even some applications, allow users to opt-in to the new version to try it out, or opt-out of the new version and return to the old one if it isn’t meeting their needs or they have a deadline and need their old workflow to meet it. Reddit and Outlook are the two examples that come to the front of my mind, but I’ve seen many more. Even my power company did it. This however is only for big changes, and usually just a toggle old|new, not fully versioned where a user can go back to any point in history. I would guess that would turn into a nightmare for maintenance, and unlike APIs, there is rarely code that is UI dependent… at least we hope not.