Possible alternative: Raspberry Pi + Modem

That's in some way the same security problem of any network management plane, there is less fundamental difference between a JunOS or IOS supervisor and a PC running Linux than one might think, in fact most of the modern network gear runs on Linux or FreeBSD, sometimes on re-badged commodity servers, with just an old-timey CLI put on top. Whether you have an SDN controller or management server talking over a network devices or you have a chassis connected to a FEX it is surprisingly similar when you get down to the details. So protecting your management plane, which has traditionally been done with local packet filters/ACLs on the device could be extended into the new designs.