Seems to be some confusion here? We used to get IFR clearances all the time direct between Glasgow, MT & Billings, MT. 166 nm. Clearance usually sounded something like "cleared to the Billings airport as filed climb to and maintain eight thousand while in controlled airspace squwak 4321 report reaching eight thousand report crossing Glasgow". The class E extended about 15 miles south of Glasgow, then the route went through about 90 miles of class G below 14,500' , thence 60 miles or so of class E turning to class C. Your IFR clearance was valid for those portions of the route in controlled airspace, you could assume that ATC would provide separation between participating aircraft in the class G, you could also assume that not all aircraft were required to participate. With (I assume the coming of ADS-B) That large chunk of G airspace has recently turned into class E down to 1200 agl as has most of the class G in the lower 48.