Hope they drop iMac out of the line. Instead, they could introduce a 27'' inch display that connects instantly to your MB or MBP via the thunderbold 3/USB-C cable and you are good to go. Why spend money for a laptop and a desktop machine when you can have the best of both worlds in one device? The cinema display could be equipped with integrated desktop class GPU so when you come back home from work you just plug the cable and have all the graphic power you need for gaming, video editing, etc. on a big ass retina display. The thunderbolt 3 offers enough bandwidth to support both the display and the external GPU within.
They may also drop Macbook Air out the line. You already have super portable, super thin MacBook for casual working, internet, photos, movies. If they update the current MacBook with more powerful CPU you already have a MacBook Air but thinner, lighter, with better display, thin bezel, etc. The MacBook Air was cool some years ago when the ultrabooks where rare. Now, it is standard for every new laptop.
Additionally, the Retina Macbook Pro would become just the MacBook Pro which would be the as in the old time for the Pro users. Drop the "Retina" tagline, because everything now is Retina, even the basic MacBook.
How I see the Mac lineup:
MacBook 12inch
MacBook Pro 13inch
MacBook Pro 15inch
MacMini
MacPro
Cinema Display with integrated GPU compatible with all of the above.
End of story.