Re: Sanity Prevails (for a change)
You can't make changes to the way the current GPS system without changing the constellation of satellites and all the millions of receivers.
I'm not sure what you'd hope to gain with bidirectional GPS (an ACK/NACK response?) but there is no way to put a suitable transmitter in all GPS receiving devices. Everything would end up looking like--and having the cost and battery life--of a sat phone.
LightSquared just figured they could push the cost of adapting the GPS infrastructure to their presence onto everyone else. It's the conservative/Wall Street/City mentality: privatize profits and socialize costs.