You can connect to 4G with your root-enabled Linux PC and a USB dongle or minipci module. Carriers don't care about your application processor, they only care about the baseband. In the case of a smartphone, you can have root access and still run the Qualcomm closed blob firmware that will drive the baseband

I doubt that's the issue. Phones already have a baseband processor and OS in control of the modem. Also evidence if viability is all the Windows laptops with WWAN.