Yes, for example mine (USB dongle) does.
Do we know specifically whether the Librem 5 will allow an external antenna. I expect you are right that someone could open it up and hack one in but let’s say for the average Joe …
I thought about that. You would need a good database of tower locations and to know which way the phone is oriented (or be able to determine that) and probably to have the logic built in to the M2M card.
You might also have to contend with a false triangulation result based on signal strength that is impossible based on which sector on each tower received the signal. Hopefully in that case the system would toss away the triangulation result. 
By hypothetical I meant it is not something that I will be experimenting with when I get my Librem 5.