There is zero chance that the Go will get faster with firmware. It should be more reliable, and voice quality will improve a bit. But keep in mind that the Go! has already been using the NEXT satellites for almost a year. Any time a NEXT satellite
was overhead that's what you'd be using. With the constellation fully complete in the next few weeks (have to move the last 10 satellites into their positions and de-orbit the old ones still) there may be some final improvements across the system.
The current Go! hardware
is limited to 2400bps data speeds.. No firmware can change that. Same for the 9555/9575 phones, and the 132kbps speed for the Pilot hardware.
The new Certus hardware will do 350/700kbps and 1.5mbps in the future, but that hardware is about $7-9K and plans are more expensive.
A future replacement for the Go! is still a ways out, probably a year, and speeds will be around 80-100kbps probably. No word on pricing or plans though.