PJ2
In terms of retro-fitting for deployable recorders and/or streaming data, I would argue against an industry-wide, regulatory requirement. All recorders in recent over-water accidents have been recovered and read with one exception, the Asiana B744 freighter loss over the Korean Straits.
And of course MH370 which you mention later
I think the case for deployable recorders/data-streaming has not been demonsrated against this accepted standard.
You fail to mention cost.
The huge and extreme cost of just recent searches for DFDR/CVR say back 5 years, is immense. But it is not set even against the aviation industry as a whole - it is borne by the taxpayers of sometimes quite poor countries. Certainly, for a short search some claim could be made that it is good training for the personnel and assets that may be in existence already, but after a few days of continuous search burning through the active life of parts and maintenance schedules, and the contracting of specialized equipment this is no longer true. I am happy to accept your argument if your airline (or more correctly your airline's insurers) as part of their operating license accept that they will fund the
entire expense incurred by the responsible country(ies), of any search for DFDR/CVR that may be necessary after a crash of one of their aircraft.
At the moment the aircraft operators are freeloading on the international community to pick up the pieces and even to organize the inquiry and tell those operators where they fell short of operating correctly. I do not think that this is acceptable given that relatively cheap simple technological fixes could reduce these costs to the international community substantially.