I'm a little hazy on what you have in mind, particularly with regard to the current rather odd preset choices (the stuff beyond jAlbum and xmp). So I guess I'd have to see the result to offer an opinion.

Not really. But then you still have to deal with other metadata entities that one would apply to titles and others that would apply to comments. You can't "toggle" something like IPTC Headline, which is sort of a "title thing," not a "comment thing."

I would rather see a straightforward set of choices: what fields should be grabbed for title, what fields should be grabbed for comment, and what fields should be grabbed for keywords. Anything less than that, IMO, just perpetuates the confusion.

Now there's a radical idea!