Right now, that particular shopping center has eight different entrances to Town Center Parkway. Town Center Parkway allows for auto connectivity to either Gate, St. Johns Bluff or I-295. There's also a pedestrian connection to Gate Parkway under JTB behind Markets at Town Center.
Would it be nice to have more of a gridded street network at SJTC, Avenues or OPM? Sure. Is it worth something upwards of $50 to $100 million? Right now, no way. Years down the road.....who knows. With that said, presently, it's obvious the shopping center does just fine "as is", meaning don't expect the developer to front something like that. Without something larger on the table (like a proposal for massive infill around it), don't expect COJ or JEA to toss in much either.
There's congestion but it's definitely not hurting business in the area. Like Millenia in Orlando, for everyone who won't go because of congestion, there's more that will deal with the extra five to ten minutes it may take to get from the parking lot to JTB, heading west on Town Center Parkway. Plus, you'll always have those that will access the area opposite the herd (ex. from the east instead of the west). There's no real congestion accessing the area from I-295.