I was looking over the two gameplay examples they showed during the first reveal trailer again, and the more I think about it, the more it makes sense for them to implement HD rumble into this game in particular.
Example 1
This one is a no brainer, dual wielding is so common, and can be done comfortably in any mode the Switch is in. Either in docked, tablet stand, or handheld modes. It doesn't necessarily need motion control ability (as the trailer doesn't demonstrate this in any way), but just the feel of the types of weapons you're using, and a focus on immersing you through these sensations.
Example 2
We know the Pro controller also has HD rumble support. It got me wondering though. Do we think it'll be dual HD rumble? One motor on the left and one on the right? I do hope so, as that would fit in nicely with the idea of maintaining the effect of dual wielding when you use this controller. It would be a really great sensation come to think of it having two unique types of rumble on either half of the same controller. For example, one portraying magic use, and the other a sword. I wonder how feasible this is to implement. But also, perhaps both motors might combine to create unique effects for the player under certain scenarios. Like some kind of object flowing between each hand, like it's passing through the controller itself. Or a more potent rumble for 2 handed weapons.
The Wii U Pro controller had a single motor and the rumble was pretty weak. I hope considering the cost of these peripherals they at least go all out in this regard and create a unique experience with them.