My take on those two questions is "No" and "Maybe".
If anything ever gets extended in the form of Sunset it will be to Orlando, not JAX. But more likely NOL - JAX will be served bycorridor trains anchored at both ends with possibly a gap in the middle, i.e. NOL - Mobile, and JAX to Tallahassee maybe, with nothing between Mobile and Tallahassee, if the states involved step upto the plate with funding either for Amtrak or their own agencies running the train.
If the Palmetto could be run more reliably on a tighter schedule to Savannah cutting about an hour in running time then it might get extended to JAX, not otherwise. I don;t really see a Silver Palm all the way to Tampa/Miami happening anytime soon.