Yes, that is the problem with the planning policy. Every UK airfield is in danger from property sharks.
If it is possible to get a planning permission to build houses, that will always happen - there is no alternative whatsoever. Every airfield where this is possible will eventually close.
It is purely down to the owner to be an aviation enthusiast and to not sell out. But his successors will invariably sell out eventually. Property sharks will always be around, circling and sniffing, and making offers to the landowner.
In all honesty I can see a lot of aviation enthusiast owners selling out too - many will get fed up with the standard level of dissent among based owners. GA is not a very cohesive group generally.
What this means for UK GA is probably that facilities will end up being either the big stuff (Biggin and above), and farm strips owned by small groups of pilots. The problem is that most strips are not and will not be owned as freeholds; most country land is owned by farmers and farmers really hate selling land if there is the slightest chance of getting a redevelopment permission one day, because they make an absolute killing over using it for farming....