Excluding interchange redesigns redesigns at Emerson, University and perhaps Bowden, I wonder if the addition of lanes can be done within existing ROW?
As for commuter rail, that would take place on the existing FEC line. However, I doubt it would be successful given the sprawled out nature of the Southside. Instead, I'd recommend lobbying for Brightline's expansion to Jax and getting a St. Augustine stop in the process. Doing so would give Jax a quick intercity rail connection between downtown and St. Augustine and set the stage for an Amtrak corridor service (assuming Trump doesn't kill Amtrak altogether).
When, and if, a corridor service materializes, advocate for stops at the Avenues and St. Augustine. Between Amtrak and Brightline, you'd end up with a defacto three station commuter/intercity rail corridor with more frequent headways than anything JTA will provide....and without significant, if any, local dedicated funding.
Then complement the intercity rail stops with the underutilized JTA Flyer BRT line down Philips to at least tie downtown and the Avenues together. This scenario allows you to market land around the rail stations and intermediate Flyer stops for nodal TOD, meaning you're getting more leverage out of an existing local transit investment. Overall, you'd end up with a poor man's scenario of Cleveland's Health Line BRT and RTA Red Line between downtown (Tower City) and University Circle (Little Italy to Windermere stations in map below).