But couldn’t this previously have happened with a Qualcomm modem as well?

You can always easily tether to your iPhone. It’s hard to imagine people who own a Mac but don’t have a phone — I assume Android can also provide tethering? Aside from the BOM price increase and physical real estate, do want to pay $10/mo or whatever for an additional line?

People have been saying for years that this has always been part of the plan.

That the only reason Apple never included a cellular modem in MacBooks is because it would raise their prices because they'd have to pay Qualcomm.

Now that they won't, it seems inevitable.