There is a very good reason to keep legacy ports on the MacBook Pro line.
The Intel Alpine Ridge controller, which brings Thunderbolt 3 to the table, will be available in two flavors :
- The first will have 4 PCIe 3.0 lanes, resulting in 2 ThunderBolt 3 ports
- The other with be limited to 2 PCIe 3.0 lanes, and so only 1 ThunderBolt 3 port.
I can't imagine a MacBook Pro with only 2 ports, furthermore when one of them would be used to charge the computer.
They could perhaps add "regular" USB 3.1 Gen 2 ports to the build to bring the total to 4, but it would lead to a strange situation where some USB-C are TB3 compatible where the others are not.
So my guess is we'll still see legacy ports on the new design. They can already make a thinner rMBP with HDMI and USB 3, look at the curvy part above and under the computer :
View attachment 578502