I'd like to point out the reason for Eastern Parkway's setup under its namesake.
The actual width of Eastern Parkway isn't the reason for the tracks sitting on the south side, but the trees dotting the northern median strip. In other words, functionality was inherently thrown out the window in favor of street-level (stroad-level?) aesthetics. In addition to being a needless roadblock for branch design (to the point of being a significant factor in my opposition to feeding Utica Avenue into Eastern Parkway), it actually makes reaching points north of Eastern Parkway and the local stations east of Franklin Avenue needlessly daunting. Thankfully, potentially flattening Eastern Parkway can address this, though construction would still require some level of disruption.