And real time latency is not "dead simple". A low priority message will always lose out to a higher priority message on CAN. With ethernet a low priority task can flood the bus if the circumstances are right.
Also, which MCUs come with gigabit ethernet?
I answered the Formula 1 MCU's (Motor Control Unit). Maybe the official one from Illmore already (I think), and some of the internal ones used for testing (which I worked with).
The NASA Space Shuttle also had several dSpace controllers on board (RTLinux with special IO drivers) and I guess modern rockets and planes also will switch to Ethernet also. It's 1MHz vs 1GHz. It makes a difference when you can afford a fast CPU, i.e. high speed controller and you don't want to wait for CAN messages coming in every 1000 cycles.