One thing we never mention about downtown (the Northbank) is, it hasn't had 5,000 or 10,000 residents living in it the majority of the previous 100 years. In the first two decades after the Great Fire, it rapidly redeveloped as a logistical hub, industrial and commercial center. On the other hand, your dense residential areas were LaVilla, Brooklyn and the ring of urban core neighborhoods like Springfield, Sugar Hill, New Town, Riverside, San Marco/South Jacksonville, Eastside, etc. that were probably twice as dense than they are today.
However, they were connected to downtown with a 60-mile streetcar network. As a result, downtown greatly benefited as being a commercialized epicenter for this urban population. When that population declined and connectivity was severed, so did the commercial prospects of downtown. The reestablishment of transit, bicycle, and pedestrian connectivity between downtown and the surrounding ring of neighborhoods is an easily first step in resolving many of the ills impacting downtown.
With that said, you can use fixed transit connectivity, just like we use highway construction, as a tool to attract market rate development along the selected corridor. This method of rapidly growing a supportive population base has worked well for Charlotte, Salt Lake City, St. Louis, Denver, Dallas, San Diego, etc. This is something should definitely be looked at in greater detail because its much easier to tap into an existing resource than the grow one from scratch in an environment where it has never really existed.
