I think I answered my own question... Is there any update on whether this would actually happen? Considering the EGLRT is almost built and a crazy amount of densification coming in plus add the Ontario Line into the mix ... and a substantial increase of population in Toronto especially in this area plus DVP always busy I think this project is a necessity at this point to get the city moving.
Why in the world haven't they actually built this? Seems to be a no brainer or am I missing something?
Leslie Street South of Eglinton Extension
When: 1960s to 1990s
Following initial suggestions in 1968 and failed proposals in 1971 and 1973, in 1976 Metro Planners brought forward a $20-million extension of Leslie Street south of Eglinton Avenue. Debates around the idea coincided with another valley-spanning proposal in the 1970s for the direct routing of Lawrence Avenue from Bayview to Leslie. Arguments in favour of a lengthened Leslie centred on eased congestion – at the Leslie/Eglinton bottleneck and at neighbouring north-south avenues – while arguments against cited ravine destruction. Another report in 1983 and an environmental study in 1984 seemingly had the now $50-million scheme moving forward, with the route involving a high-level bridge over Wilket Creek Park, followed by a road along the CPR Belleville line before emerging at the Bayview Extension near Nesbitt Drive. Citizen groups argued that, if allowed, the Leslie proposal would re-open the Spadina Expressway debate. In 1988, Metro Council voted in favour of the 4-lane extension, but the price had gone up to $74 million dollars. Debate and public consultations continued into the 1990s with no extension built. In 2000 and 2002, Toronto Councillor Jane Pitfield proposed lengthening Redway Road to Bayview. Opponents feared the damage to Crowthers Woods and a rehashing of the Leslie debate, and nothing came of that plan either.
Source: 
https://scenesto.com/2019/10/15/roads-never-built/