Post MH370, are there developments to improve the tracking of airliners?
No, no technology has been developed that utilize the smartphone of passengers because the airplane is at a location where it is outside the connectivity of any smartphone during the entire flight, except for maybe the first and last few minutes.

A smartphone needs a cell tower to establish network connectivity, which typically has a range of a few hundred meters or at most a few kilometers. Once a plane takes off and climbs to around 5000 feet (which takes only a minute or so), it is out of range of all cell towers. There are departure and approach paths which flies over populated areas, but most flies out to rural areas for noise reasons. And if a plane is over a populated city, you don't need smartphones on board to track it anyway.

The only hope of communication in the middle of an ocean is a direct connection to a satellite. Smartphones are not equipped with the necessary hardware to do that, and I doubt they will in the near future. To connect to a satellite, you will need to know where it is in the sky, which in turn means you need to know your location to a reasonable accuracy and an antenna to point the signal at the right direction.



Your idea about inflight Wi-Fi is an interesting one. Theoretically, if someone's cellphone is configured to report its location once in a while (to help in a situation where the phone is stolen or lost), and that cellphone is connected to internet, it can be used to track a plane's location. However, bandwidth onboard is limited to the Mbps to Kbps range, since it is a satellite connection. In fact it is so limited that you have to paid (quite an expensive price) for it.

Moreover, this solution does not solve the connectivity problem, because the phone needs to rely on the plane's satellite connection to establish connectivity. But there needs not be a phone - the mere act of connecting to a satellite is already enough to track a plane's location.



However, there are changes in the aircraft systems that will allow airliners to be tracked more accurately. For example, ICAO recommends that by November 2018, all aircraft over open ocean should report their position every 15 minutes.