I think that's a great idea, and I have no doubt that it would be regardless if Amtrak OR Tri-Rail end up using the FEC tracks. Not to get too deeply into the Tri-Rail discussion, which always seems to get threads locked, but if Tri-Rail were to stop there, it would provide a decent train-to-the-plane alternative. I say only "decent" because Tri-Rail, since it runs north-south, would not help out those who live in the western suburbs.
While it's a great idea for Amtrak to stop at FLL, I don't think Miami-Dade is going to be particularly keen on Amtrak suddenly pulling out of the MIC. After all, Amtrak terminating there was one of the reasons (but certainly not the primary one) for building it.
Still, if Amtrak does shift over to the FEC, a downtown Miami station around where Noel suggested would have excellent transit connection possibilities. If the station were built
here on NW 1st Avenue between NW 5th and NW 6th Streets, the Overtown Metrorail stop would be directly across NW 6th Street and the now poorly named Arena State Plaza Metromover stop would be directly across NW 5th Street. Obviously, a two-block spur would have to be built where the FEC tracks curve east to the port south of NW 8th St. (and NW 6th Street would probably have to be closed there), but I believe the FEC still owns both parcels on which the spur to the terminal would be built since it is the ROW of the original tracks that went to the old station north of the courthouse. Perhaps the spur could even be elevated so there could be even easier walkway overpass connections to Metrorail and Metromover.
Also, and this is much farther out since Beach political hacks put the project in the deep freeze for another ten years or so, but
Baylink is or was planned to have a stop right at the very corner of this possible terminal. That would be the ideal situation because most tourists coming to South Florida stay in South Beach, where one does not need a car. Indeed, most of the people coming by train are already inclined toward traveling this way, so it's a natural fit.