I couldn't see it being upgraded at all north of where US 61 meets 110. If anything, I could see a route running along river road from a new bridge north of BR to LA 1 near New Roads, and then following LA 1 with freeway upgrades here and there as bypasses, as a route from Alexandria to Baton Rouge, but that would be a waste of money. As far as a BR-to-JAX route, I-12 and I-55 do a very good job of it, as stated above.
How many people honestly go from BR to JAX that would benefit from a new route? I could understand a Natchez to McComb route to serve long haul trucks going from northern Louisiana to New Orleans (a northern I-49 South, if you will, allowing trucks to bypass Baton Rouge while shaving time, along with motorists), but not Baton Rouge to Jackson.
In other BR news, why on earth does St Phillip St create a rarely-used left turn lane while making through traffic narrow to one lane? There's no reason why you can't have two lanes going onto Nicholson. NONE AT ALL!!!