Starting mavlink on same device as used for system console

The NuttX shell is opened on device /dev/ttyS0 and this is started when I boot up my board. Do any of you know if it’s possible to start mavlink on the same device (/dev/ttyS0) at the end of the rcS script (mavlink start -d /dev/ttyS0 -b 115200), essentially replacing the system console with a mavlink shell? The thing is that I only have one serial device on my board, and I would like to have the mavlink shell instead of the NuttX shell. But I’m not sure if this is possible?

If I run the “mavlink start -d /dev/ttyS0 -b 115200” then it seems like I’m able to receive the HEARTBEAT, but I’m not able to get anything in return if I send for instance the “?”. So it looks like a one-way communication to me. So I’m wondering if this has anything to do with that I’m trying to use the same device for both system console and mavlink. Any good advice?