Could you encode data in a Black Box ping?
Current underwater locator beacons (ULBs) have a detection range of only a few km. 16 km would be under exceptionally favourable conditions. So in most cases the GPS data would not be of any additional help. It might tell you where the aircraft was before it hit the water, not exactly where the debris ended up after falling through several Km of water.

An advantage of current ULBs is their extreme simplicity and small size. There's no need for external data-feed and power connections. There are no issues of openings in the casing for waterproof connectors that also need to withstand the g-forces and pressures expected to be endured by a ULB. They are easy to test regularly and relatively easy to maintain.



From what I have read, current proposals for improvements to ULBs mostly focus on


increase duration from 30 days to 90 days
increase range by changing frequency from 37.5 kHz to ~10KHz


There are trade-offs here - longer duration means bigger batteries. changing the frequency may make it harder to distinguish from other sources of sound in the ocean.



An interesting 2011 dissertation describes the difficulties involved  and discusses modulating the beacon signal to include data.