I remember investigating this feature at least ten years ago, maybe more. I made a post on one of the walking or technical forums about the little known Memory-Map tracking application that worked in the same way as Viewranger BuddyBeacon, displaying the current position on a PC/Phone screen on OS mapping to anyone logged in with the username/PIN.
I expected considerable enthusiasm but the post didn't get a single reply, nobody was interested.
Anyway, on the technical side, these solutions have a fatal weakness: they rely on the cellphone network. If there's no phone signal, which is often the case in remote areas, it's game over. Yet this is exactly where it would be most useful.
To be effective such systems must work via SAT. The SPOT satellite tracker was launched with much fanfare about the same time as MM Tracker and appeared to offer a great solution, sleeping most of the time but waking periodically to send a location via SAT to a server, hence it had a superb battery life. The experiences of testers were mixed to say the least, some reporting that the many of the broadcasts were never received by the server - there is no receipt acknowledgement for a broadcast.