I would love to have both server/social location sending as an option in apps both in a invisible mode and also sharing my location, though since the N900/Maemo culture is naturally disruptive we should consider for situations where internet is not possible SMS would be cool.
Lastly, and this is going out on a geeky limb, if we could do DTMF or PSK encode/decode import/export that way we could even quickly share location via wired telephone or walkie-talkie radio.
Lastly maybe include some encryption so it can be used by displaced refugees, for example the 100,000s in Syria, to meet up without fearing that their shared location could be used to endanger their lives.
AFAIK the code is all around already here on TMO, I just don't know how to splice the functionality together to make what I think many of us would find very useful.