How else do you propose they shave off enough from the cost to manufacture the thing to make a material difference? It seems to me that overhauling the original device will start with the controllers.
Since it would be a smaller form factor, a smaller screen, for one.
It would also mean removal of the motion IR camera, since a portable only Switch would likely lack detachable Joycons.
That also means no need for separate batteries for 2 Bluetooth controllers that snap to the side of the device.
Since games would be running in their respective handheld modes only, they could skimp on the internal hardware components so that they only achieve the maximum outlined performance for handheld mode.
That's a hell of a lot more savings than just taking out HD Rumble.
Skyward Sword didn't work without Motion Plus. While that constitutes a "reverse pattern" of sorts, if the market ends up dictating that "lower price point/greater portability">"presence of HD rumble as standard," then Nintendo will find a way to make the rumble-less SKU the base SKU in the interest of popularizing and selling the platform. If we're talking a year or so down the road, it wouldn't be inconceivable. Are there no early 3DS games that REQUIRE the 3D function, for example?
As outlined above, there are many things that can add up to a cost savings without taking out features that would be available to standard Switch games in handheld mode.