I use dating apps regularly when traveling for exactly that. You'd be surprised how willing people are to meetup without the pressure of dating/sex being involved. Fly into a city for work, meetup for fun, and make a new friend for next time.
1. People tend to only join other established groups rather than message individuals.
2. You can only send a hello to someone else and hope they see it or respond back (you can't even look at their profile from the Hangout section). Mostly, they won't respond.
3. Hangouts allows the same person to join as many groups as they want, even though the suggested events are happening at the same time.
4. Just like regular CS events, most people that say they will go often do not show up.
They need to seriously fix all that and develop it into its own app to flesh it out.