Agreed. Jonathan's "maybe" had a hint of doubt to my ears, like he was conflicted. And like you said, we don't know if that's his whole response or if the rest of it was cut out for the purposes of the trailer. Personally I like the idea of Jonathan not having all of the answers. I'd rather have Clark discover his purpose on his own, using lessons (both good and bad) from both Jonathan Kent and Jor-El to do so.