Picked up the kata 3n1 the other day with the other gear.  I’ve been looking for a sling forever, but one you could ALSO wear as a backpack.  While the kata isn’t perfect (no bag will be until I make my own) it’s damn close.  You can wear it as a sling EITHER WAY, a backpack, or cross the straps for a different approach (why I don’t know).  Also, the straps not in use hide very neatly behind the back portion of the bag.  It’s got enough room for my longest lens and 4 others with any body which is perfect.  I’ll see if I actually like using a sling/backpack, but if I do this is the best option for me.