Sallyanne, keeping streams separated and communicating through satellites is a done deal. Back in the 80s it was a done deal on the DSCS satellites and ground stations. As you say, it requires a proper protocol. It's been invented already, several times. Inmarsat M is another protocol which manages this.
Existing systems
cannot provide this requirement which is for continuous, fast and reliable data simultaneously from hundreds of aircraft moving at high speed. Ask any provider for a quotation!
Volume is a problem. And price is a problem. And spectrum is a problem.
Yes, as has been said
ad nauseam. No-one has said this can't be done. Only that it is not an economic proposition.