2. Professional photographers for a long time primarily used CompactFlash which has never had built in hardware support. So I can't imagine they are suddenly missing something they never had. It's the prosumers who were the heavy uses of SD cards and who were inconvenienced with the decision. Although most cameras come with WiFi these days so you can see Apple's thinking in removing the port.
3. Using a SD card as external storage is an awful idea. It was never designed for that much IO especially on OSX which can thrash storage devices pretty badly (check fs_usage). Just buy a USB-C enclosure and a 2.5inch hard drive like everyone else. Very cheap and comes in large sizes.
The old Model (15") (no new processor + no usb-c)
Isn't this the same argument people used when the Mac ditched the floppy, and then again when they ditched the CD-ROM drive?
Edit: Oh and also lack of CUDA support i.e. NVIDIA cards.