Actually, Apple's App Store guidelines do prohibit duplicate apps. Even so, here are some reasons not to do this:
1) The apps would become separate installations on your device, with separate data, and no built-in way to migrate data between them. So if you were running the current version, and then decided to install the n-1 version, you would have to reinstall all the data into that and reenter all the settings.
2) You would have to pay separately for the two versions, including all the in-app purchases. I would predict much anger directed toward me if someone had a problem, and wanted to install the n-1 version, and found out they had to buy it again.
3) Many first-time users would be confused by the two versions in the store, or install the n-1 version instead of the current version, which would defeat the purpose of this scheme.
4) My app release workflow (which is easier for Android but can be very difficult for iOS) would be doubled for every release, requiring significant additional time that could be spent improving the app in other ways.
I know from experience on other issues: when Apple or Google decide that they don't want something to happen on their platform, attempts to work around their wishes are not likely to be successful.