Both streets can and should be retail-lined. Driving along main, it feels there is almost an equal amount of (admittedly decrepit) retail space along both streets. It also feels like there’s more ad-hoc retail on Main; In the West, there are plenty of homes-turned-shops/private offices.
I’ve also generally heard the sentiment (here and on SSP) that the main (pun intended) boon of both two-way conversions will be that Main is unlocked as a major street rather than thoroughfare- it may become more desirable than even King for developers. King is certainly hampered by being a one-way, but it is more vibrant than Main, which is definetely second-in-line and more barren as a result. Thus, it has significantly greater potential, and has definetely caught the eyes of developers.
With that said, I understand the hesitation to build retail in the West; Main st will still be the main 403 access point and thoroughfare in the West end. I expect little retail at least until about Locke- since that’s where you really get into downtowns influence- unless the city takes initiative on that front (they won’t). Through the core however, Main st without its shackles will be so different that developers will jump. Vrancor already has, despite his retail units sitting vacant right now.
Edit: Oh, and this project looks ok I guess. While we’re perhaps past our era of commie-block, cost efficient condos, taking up Toronto’s setback cues is a bad idea, not the least because we can’t execute them nearly as well (which isn’t that great to begin with). You copy a C+ paper and you’ll end up with a D. However, the end of truly bottom-barrel materials is welcome. Makes up for these shortcomings imo.