I think jRPGs and wRPGs (western-RPGs) are meant for different experiences. jRPGs tell a story, and a lot of them do this really well. Final Fantasy, Chrono Trigger, etc., have all focused on telling the story that they wanted to tell. Is the combat engaging? Sometimes, but it's a limited system. (In Final Fantasy 7, I felt that the meta-combat (combining materia to make more-viable spells) was more entertaining than the menu-driven actual-combat). Most importantly, it's a story about a character.
This is in stark contrast to wRPGs, which tend to tell a story about you, or the open-world style games where you tell the story. The combat tends to be more engaging (debatable, obviously), but the story is limited by the open-world-ness, if that's a mechanic, or by engaging the player in the story that is about them (this isn't impossible, it just tends to be done poorly, I think).
jRPGs often have an open-world component (most FF games once you get the airship), but it's a relatively small component and really serves one purpose: getting everything you missed.
I think that trying to combine these genres, based on their strengths and weaknesses, is going to make for a pretty weak game (though I'm very often wrong).
A lot of this was inspired by the Extra Credits videos; these are not all my ideas.
