There will always be a dongle problem. USB-A is not going to disappear for years because for many low IO devices there simply is no benefit to change to USB-C. And as an academic, I can tell you that I have NEVER been to a conference where the expected input for the projector system was not VGA. For the past 10 years, I've had to travel with a variety of different XXX > VGA adapters. USB-C on the MB and MBPro means I have to buy yet ANOTHER one, but also a dongle for an SD card reader (currently built in in all my other Apple devices), and a USBC > A adapter for a clicker. So, not exactly impossible, but annoying nonetheless.
I can't ever see projectors becoming USB-C as standard unless there is a way to upscale to USB-C from an inferior output source (e.g. DVI, miniDP or VGA).