Right to Left English for left handed people
You'd have to use a custom ROM to do this, because the layout direction is a fixed part of the locale information, not a user-visible setting. Even if you could, you'd find that most apps wouldn't change. It takes development and testing time to make Android layouts bidirectional, and the support wasn't added to Android until Jelly Bean, so apps tend to only use it if they actually do support RTL languages.

Even on apps which do support it, you'd probably find strange behaviour because English isn't supposed to be laid out right-to-left. For example, text labels that are too long might have the "..." at the start instead of the end, or vice-versa.

So in summary, it's a lot of effort to end up with a broken configuration.