I don't think you quite understand what this is. Unlike vertsms, this works everywhere you have text input - it's a regular virtual keyboard, not a separate application.

Vertsms is really not a good way to do things.. asking every application to implement its own keyboard (or creating separate applications for portrait usage) is not a productive way to do things, as it either involves duplicating whole applications, or at the least, everyone creating their own keyboard solution which looks and feels slightly different from everything else. That's the whole reason this exists.

That having been said, if you'd taken a closer look at the initial post, you would notice that 'fast predictive input' is already listed under 'future direction'.

Thanks!