While I agree the new plugin would be nice to have (and I would certainly use it), couldn't you just run the command from Squeak using OSProcess as part of the initialization?
Not really because we can have several USB boards connected at the same time, without knowing, a priori, their number (ttyUSBx). We have an automatic detection mechanism : we write on the first 10 COM ports a string and read an answer when one of our board is present. Works fine under Windows, but under Linux or MacOS... I could link *all* the ttyUSB to the corresponding ttyS, but... well... it's a bit dirty :-) and could bring some conflicts if traditional serial devices are plugged and already use the ttySx.
Severin