While I'm all for this, I think the main issue with plazas is that a majority aren't in bike friendly areas, at least the ones I can think of. I mean if by plaza you also include strip malls, those aren't usually in areas with good pedestrian sidewalks or safe cycle lanes. Even in nicer, pedestrian plazas that aren't in a city centre, those still tend to encourage customers to arrive by car before walking around the path. There needs to be substantial improvements before these plazas can really encourage cycling. Bike racks alone won't be enough.
Though purchasing bike racks at the very least or as a start would be a step in the right direction.
I, myself, live downtown Toronto so bike infrastructure is plenty (though of course can always be better). That said, the further from downtown the less hospitable it can be biking with large roads and less road law enforcement that has some priority for biking. Then there's the suburb towns that are only now considering really bike infrastructure and areas outside the GTA that are nowhere near building it. I agree it wouldn't hurt anyone to have bike racks around as a start, but it shouldn't be the only starting point if we want people to really use them.