Filing this against libsigrok though users will perceive this issue from 
either of the applications.

When drivers require or support the conn= spec, the current implementation 
is rather strict and expects a full user provided value which connection to 
use to communicate to the device. Usability could get improved by accepting 
abbreviated serial port specs like ttyACM0 instead of /dev/ttyACM0, as well 
as ambiguous values like ttyUSB when multiple devices are connected to the 
same kind of serial port and all of them should be used.

There may be individual device drivers which support this feature already 
(uni-t dmms come to mind, though not all of them universally). Ideally the 
feature would be common and applicable to a larger set of drivers. Neither 
is this limited to serial ports, could also apply to USB VID/PID specs, or 
BLE address specs, etc.