All of the upgraded line between WPB & Cocoa will be at least double-tracked. Most of the new construction between Cocoa & ORL is being built single track. Bridge abutments are being built to support double track, so when they decide to double-track those segments they'll just need to add a parallel span.
Not sure, but I think track geometry is the primary speed limiting factor between MIA & WPB, but also grade crossing protection on that section has not been upgraded to the requirements for 110 mph. I read that some curves between WPB & Cocoa are being realigned for higher speed.