Pretty bizarre idea to completely ban one form or another like that.
Personally I'm not a fan of wasting that much land on *2* vehicular accesses to a property - a street AND a back lane is just that much more concrete for the same living space. Seems even more auto-centric. But some prefer it, so let them both be built.
About the only sensible "all back lane" style that I've ever liked was some streets I saw in Winnipeg (copied from somewhere else) - all houses had back lanes only, but their front yards had no street in between. Creating a wonderful greenspace between the houses, with a nice sidewalk running down the centre.
Bad quality picture, but gives the idea.
Not sure what this whole "eyes on the street" thing is supposed to protect, anyway. Forcing everything into back lanes just means the "bad guys" go there instead. Plus, at least in modern (past 30 years or so) Calgary developments, back laned houses typically have much larger back yards than front - so people still spend all of their time in the back yard. Next to their garage/driveway...
If anything, I'd rather see the City try to stop this "every single lot must be completely fenced off from its neighbours" mentality. I loved living in a house where 10 or 12 neighbours all had no fences, and you had this wonderful greenspace in between all the houses. Now everyone just jams themselves into a tiny postage stamp yard, walled away from ever seeing your neighbours.