They will leave the laptop with only one port. Why? it cost less to do so... And they can sell hubs/cables afterward.
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I doubt the difference in cost is meaningful. I think it has much more to do with form factor. There simply isn't enough space anywhere on the rMB to put another port, except for where the headphone jack is now.
USB-C is a standard and Apple won't be making much money from USB-C accessories except for the people who buy them at the Apple Store out of convenience or sheer ignorance (that they can be purchased elsewhere for cheaper). Whatever revenue Apple was making from selling proprietary chargers will disappear.