The thing you must remember about aromatics is that not every flavor/scent will work as an aromatic tobacco. Vanilla works well; it's easy identifiable as vanilla and it doesn't get in the way of tobacco. Contrast that with chocolate. Sure, there are a few blends with chocolate, but none of them really taste or smell like real chocolate.
Berries can work, but when was the last time you saw watermelon tobacco? Caramel, si. Marshmallow, no.
Coffee smells great, but have you ever smelled BURNED coffee?! Not the same.
If you like hazelnut coffee, then why not just enjoy one with your pipe?