The BDUK funding is meant to be used to get 2 Mbps to everyone, and a target of superfast to 90%.
The question of whether Openreach plan to do your area commercially will be known to the county council as part of the BDUK procurement process. Some councils have released useful maps so you can check.
It is probably a case of waiting for the council to announce their project and then can pester for details of the plans.
There is nothing to say that the funding cannot be used for denser population areas, in fact in terms of bang per buck the development sounds ideal, but raises question of why developer never considered this as part of the original build.