Openreach are too large to be reacting to small players enabling little pockets of houses. They are building to ~300k houses each month and deployments will have been planned years in advance.
You will get FTTP from Openreach because pretty much everywhere is going to be enabled, but the amount of time this takes won't be affected by another provider being there.
People who post here aren't your average user. Zzoomm packages start at £29 for 150Mbps symmetric, for a lot of people the option of paying Vodafone £20 a month for 40Mbps FTTC is preferable to them, so the presence of what we might all see as a superior service doesn't necessarily mean that Openreach wouldn't still be able to make money from a certain area. Maybe people want to stay with Sky because they supply their TV, maybe they think BT are the best provider, maybe they want a landline which Zzoomm don't seem to offer.