The big bikes will be cushy rides on good, fast roads. And they can haul a bunch of junk along with a rider.
The big loaded bikes can be a pain when trying to explore off road. What usually happens is that the rider realizes it's no fun picking up the heavy bike and/or handling it in precarious situations, and then he/she stops exploring more of the off-the-beaten-path places. If it hurts to scratch your butt, you stay away from that pleasure...
What we call a mid-size bike, 400-650cc...?, is known in many parts of the world as a big bike. The reason why is that they do not need a bike of that size to run their local roads. Overkill.
I predict that we will see some mid-size bikes marketed towards adventure riding in the not so distant future. Not a new idea, just new ads for an up and coming market that's been mislabeled.