Hi, SLF here, lurked for a long time and followed the accident since day one, but this is getting silly...
If the problem is finding a black box at x thousand meters underwater, the obvious approach is not to stream all data realtime over satcom, but to actually address the problem at hand.
The black box(es) could quite easily be given a gps antenna and a bit of intelligence to be able to derive that the current trajectory will lead to impact in seconds (100m altitude decision point?) and explosively detach from the airframe. You make them float and give them a radiolocator SOS beacon.
They could even then track their trajectory on the sea to help locate the remains on the seafloor.
If you want to make it an incremental upgrade, you make them duplicates of the original black boxes already installed on the plane, that can't be that much of an engineering challenge, surely.
In this case, planes were overflying in very short order, and vessels were onsite in 6 days, in the middle of the atlantic, so radiolocation would be a cinch.
One could say that this gets complicated over land as altitudes over mean sea level (MSL) obviously vary greatly, but there are few areas below MSL on land (they can be programmed) and over land it doesn't matter as the normal black boxes are usually located without issues, and the worlds oceans don't vary 100m from a standardised geoid
AFAIK.
If you want to be uber modern, they could squirt the data to satellite after the fact, but I feel that that is overkill.
If there is a false alarm and the pilots miraculously recover the aircraft in those last 100m, they can relay a message to disregard the SOS and have it replaced upon landing.
Sorry, probably missed lots of obvious stuff, but felt compelled to post.