Is that really the process? When I see an area like Homerton becoming 'gentrified', I see rents zooming up first, followed by the (rather slow) ingress of new businesses. tbh it's not really become gentrified. It's just become unaffordable.
But to the extent that the process you talk about does happen, Foxtons will jump on any improvement in an area to talk up prices. That's the real evil of the process, imo - the impossibility in this model of urban regeneration without it turning into gentrification. For example, if an arts and crafts centre were to open in an area, providing spaces for artists and artisans at affordable prices, performance areas, exhibition areas, and loads of free activities for kids - ie something that I think few would say was not good for an area - Foxtons would leap on it as an excuse to put prices up.