bizman, in the case in front of us or anything similar there is not much that would have gotten searching started much sooner. The area was enveloped in a heavy storm. And that's very likely one of the conditions necessary to have made this plane fall out of the sky.
It is also probably coincidence that the plane dropped out of the air with as many ACARS messages as we see. And there seems to be nothing in the ACARS messages to prompt a person to assume the plane hit the surface except the cryptic cabin pressure message. You'd have to have some VERY expensive software involved to get maybe a 20% to 40% detection ratio. You'd have to have a very well trained and analytically minded person sitting feeling his brain ooze out from between his ears from boredom scanning the incoming ACARS messages and trying to guess which one means plane prematurely contacted horizontal surface. (You don't have enough money to get me to do that more than one day. An airline might be able to find enough money to pay me for maybe three weeks. (It would be broke afterwards.) I might do it for four weeks if I came out of it as unquestioned dictator for the entire world. So I don't see it happening.)
There is a practicality gap here. There is an effectiveness gap here. There is a huge cost benefit gap here.