[ydant]

They sort of did - they had a "request check-in" function. It never worked very well.

They also had an accelerated and supposedly more accurate tracking option on demand (i.e. I could request my wife's location to be updated "in real time"). That never worked very well and was removed.

[ewolf]

That's strange — I've always had the impression that the battery usage of GPS was the main obstacle for location tracking services, so that any way to sidestep expensive polling would be a greatly welcomed remedy. I can't imagine that this would be technically impossible.