Bearfoil (re 1810), satellite radios don't work every time. As a near life long amateur radio operator radios don't work a staggering amount of the time somewhere in the world. HF relies on the vagaries of ionospheric bending. VHF goes right through the ionosphere except in strange equatorial conditions when it ducts and you get taxi radio interference with taxis in the ducts in Hawaii and Southern California. VLF works over long distances if you invest in enough wire. You can't do high data rates for burst transmissions, though. Heck, that is a problem on HF, too. Multipath ruins most fast transmission modes. 10,000 bps is blazing fast for HF and requires a not insignificant amount of time to achieve lock.
Worst of all, satellites are not there when you need them. If your first awareness of a problem is the plane falls off on a wing in a massive stall - and ACARS goes off beam to the satellite. Worst yet, you are about mid way on a route between Perth and any place in South America - you are over the South Pole. You have no satellites to speak with. Look at mm43's satellite coverage maps a few messages on.
Now duplicate this on any of the air routes over the North Pole.
Add in auroras and HF goes dead for you. And on a guess I'd not want a substantial fraction of a mile of wire hanging out in aurora conditions unless there was a REALLY good way to drain off static electricity. But that last detail I am not sure about. It's an honest hunch. VLF might get through the auroral murk.
If, while you are out of contact with ANYBODY all alone for hundreds of miles in any direction who will hear your emergency transmission on 121.5 MHz or 405MHz or even 2175kHz?
This is why I wonder, "What expense is worth itself as a partial solution to the missing flight data situation?" A patch here to solve AF447 still leaves us open somewhere else if it relies on data transmission to satellites or passing ships or nearby aircraft.
I also note that so far as I know it is "easy" by some definitions of easy to transmit a mayday on 121.5 MHz and supposedly every plane in the air is monitoring the frequency. Nothing was heard. Was a transmission attempted and swamped out by various kinds of static discharges in the area a couple hundred miles around the aircraft? If the plane happened to be in a duct there could have been nobody at any place along the duct to hear it. And nearby planes would be less likely to hear it due to attenuation - signal lost to propagate in the duct.
Radio is a nice solution. I do not believe it is a comprehensive solution to this problem as proposed so far. Modified ELTs for over water use might be a good radio solution, however. (I'd propose "ejected on impacts more than 3g, floats, is wired into navigation to receive up to the second updates, and transmits that location every 20 minutes at 50 mW on 121.5 MHz FM using APRS formats. Then I'd work out the math to see if it really would work and could be setup to both float, survive impacts, and last a month.)
But none of this finds AF447 for us. It "only" makes it harder to recreate some lost recorders situations.