I admit that a generic gamebook engine might be cool, but believe me, it would be a lot of work! Because even with fixed rules like in LoneWolfDS, there are many specific cases to handle everywhere.
So allowing authors to add many subtleties in their own books to make the adventure enjoyable would require a very powerful and flexible engine.
Even if I made my engine with flexibility in mind, a generic engine is another step ahead. So for now, I'm afraid I'll stick to LW. ;)