> It runs on your keyboard, so it is always active no matter what software.

I like the idea, but wouldn't that get annoying in contexts where you don't want it? My text editor already annoys me with auto-correct, I'm not sure I want even more of it! Ideally, I think this would be an OS-level feature, but one that only targets specific contexts (e.g. 'rich text' fields, not 'plain text' ones; configurable at an app level).