Looks like http://openadaptxt.sourceforge.net/ is not actively developed, though.

I would suggest to look into Ubuntu Touch solution. They had predictive text input and, as far as I understand, use the same keyboard stack as SFOS. There was someone who was looking into it earlier, but I don't remember the name, unfortunately.

We had some discussion on it in this thread (pages 54,55,56,57 - between other messages). OKboard was suggested and it may have some text prediction in it already