Syed " What do you think would be the killer app, from a content perspective? Simply sending a comprehensive set of grib files? Or something else?"
For people that cross oceans then grib weather forecast files would be essential.
But sending a broadcast every 6 hrs or 12 hrs with a world wide grib file could be something like 1 - 2 mb every 6 hours Assuming you want to send out most of the world.
But if we broke the grib up into the 3 regions as defined by Inmarsat then it would be a lot less information. Mariners at sea are only interested in their geographic regions grib. Possibly this could break the grib down to .6 to 1 Mb per region or even less.
It might be possible to use a special compression algorithm and remove a lot of redundant information as the current system is sort of designed to be a one off, stand alone data file but you will be using apps that could handle date , spacing etc so this information could be removed from the data set.
It might be possible to remove grib data from a worldwide grib file where the wind data is over land. This might reduce the data size by a third.
I think this kind of thinking on reducing grib file size has been worked on. I am hoping some of the excellent mariner programmers from the Opencpn project will get behing the Outernet Grib project and possibly something like a Opencpn Outernt Grib plugin could be born.
The open source navigation project Opencpn already has a Grib plugin and a RTL-SDR dongle plugin.
It might be possible with the grib file forecast to have the first four 6 hour forecast and then just give 12 hour forecasts. So a 3 day forecast would have
4 X 6 hrs day one
2 X 12 hrs day two.
2 X 12 hrs day three.
This would still be very useful for mariners.