What an interesting article. As you say, there are plenty of different angles on this. The actual mechanism of the land seizure would be something that will determine the response from land owners, I suspect. One can only presume that the owner will have some warning before the process commences and that the government will not sensible be able to simply take possession of a private owner's assets.
An over simplification perhaps, but at the sniff of a land grab the owner need merely use the newly relaxed brown-field rules to start the planning process themselves. This will presumably stave off the seizure at the same time as multiplying the value of the land by a substantial factor for the owner. (If planning fails and is subsequently granted to the government after seizure, there will be some interesting test cases in the courts!) After planning is achieved, and assuming that there isn’t a sudden disinterest from developers, it should be a win-win for all concerned.
This is not to say that I, for one, would support governmental intervention by an over controlling legislature, but it will certainly stimulate the house building market. Food for thought, as you say.