The main issue with Ferry Road is it pinches down quite a bit when it hits Inverleith Gardens and at several other points after that on the way into Leith in a way that would require a level of rethinking the cooncil have always shied away from when they have the nice convenient not-driver-antagonising railway path running parallel.
TBH North Edinburgh as a whole is a bit of a ****show because there isn't any really contiguous stretch of wide road suitable to complete an outer ring road with the Bypass, so the only way I can think to really fix it is to be quite radical; a circulation plan that shunts traffic East out to the Bypass through Leith and West out along Telford Road to Maybury Road, with everything North and directly South of Ferry Road turned into a series of LTNs, and Ferry Road itself thoroughly filtered between Granton Road and North Junction Street with a mix of one-way turnoffs for residents and a few bus gates(eg bus gate the entire area around the junction at Inverleith Row, which is currently a pollution hotspot - combined with removing a lot of parking that lets you turn the Row itself into a N/S active travel and public transit corridor into the city centre).
Don't know that even the Greens are willing to go as far as that kind of plan though.