Apple better not waste space on an optical drive!
You can always add an external burner if you need one. (who should be using USB sticks at this point in all cases anyways..)
If you don't need one an optical drive, you CAN'T just make the device smaller by removing it.
It becomes wasted space!
I don't think people are using optical discs so much for data transfer. You're right... USB sticks are much more suitable for that.
They are more likely using optical discs for DVD production or audio CD burning.
But yeah... if the new Mac Pro doesn't come with an optical drive... you can always go external.