The expense of building an unneeded river crossing would easily kill both of these projects. If we want an extra crossing for bike/ped, perhaps we should consider something like this for the Fuller Warren between Riverside and San Marco?
With this option I doubt that you could maintain sufficient vertical clearance beneath the bridge. It would be more practical to put a barrier separated bike lane on the existing bridge deck.
With commuter rail on the FEC bridge, I wonder how you could maintain capacity for existing or projected levels of freight traffic.
Nashville and Chattanooga have both made pedestrian bridges out of obsolete or redundant structures. Both bridges have contributed to the vibrancy of their respective downtowns. If the FEC bridge ever becomes obsolete, I would like to see it reused for bicycle and foot traffic.
If it ever becomes redundant or obsolete, I'd like to see the same outcome for the old Shands Bridge between Clay County and St. .Johns County.