I think the OP has a point, unless I'm mistaking his question (although I understand StoneyB's correct answer given the scenario in the first line of the cited question).
Scenario 1: A mugging victim is giving her report to the police.
The assailant approached me from a poorly lit area near the park benches. I did not see him until it was too late.
Scenario 2: An editorial in the newspaper a week later, about that mugging, and others.
We have been asking for improved lighting in the park for several years, yet City Council has done nothing whatsoever to make the park any safer. What would have happened last week if the area near the park benches had been well lit? We cannot say with any certainty, of course, but the victim might have seen the assailant sooner——and she might have been able to turn and flee.
In the question cited, about demolishing the park, the demolition was under consideration--a possible future event. The tenses asked about make sense only with a possible|hypothetical past event.
Are you saying that What would have [VERB]ed if this park had been
[VERB]ed? question is right, if the demolition had been (Is this had
been right?) been a possible PAST event, BUT is no longer considered?
Also, is the construct wrong if the demolition is still being
What would have happened last week if the area near the park benches had been well lit.
What might yet happen is of no consequence to the choice of tense there. Ongoing discussions about adding some lights to the park have no bearing whatsoever upon the events of last week. The relevant hypothetical situation is situated in the past.
What would have happened last week if the park had been well lit?