Ah gotcha, I thought by “two channels” you meant USB + UART.
Check out: Using UART on a brand new Nova Global Cellular Modem - #6 by tve
With the current layout the 5V is sent to the Nova disabling UART, you will need to provide seperate 3.8V pads (to use without USB plugged in) or have some sort of switch to still use the 5V to ~4V converter from Hologram but remove 5V from the VUSB pin on the SARA.
Last suggestion is it may be worth putting a level shifter or atleast a 5V tolerant buffer between your UART connector and the SARA. I think its likely people will mess up and hook 3.3V or 5V logic up to the Nova UART pins accidentally.