I don't think the Sumo is a fad, but I don't think it's as versatile as you say. Went on longer trips on a Husquarna and I felt that a dual-sport would do better. For normal street use, why not a standard bike? Its very true that they are agile and easy to learn on though. And any kind of greenlaning favors the Sumo/enduro.
So, Sumo isn't that cool, but they are not lame either in my opinion. I'd just go for a dual-sport like a GS instead if I would use it like I used my Husky. Which is mostly road.