Inversion is used to emphasise the negative aspect of a statement and so it would be strange to invert in neutral, factual, speculative situations like yours. I recommend that you only use inverted clauses at the beginning of a sentence for dramatic or literary effect like in this example: "Never has any tactic been so impractical for schools to implement." (Wow! Shock, horror!) The second one is correct but unusual and I see this generally only in literary contexts. The kind of sentence I have written below is more common in other formal contexts: "Were all buildings to be painted white, residents would feel scared." In this sentence, we are talking about a hypothetical future scenario of buildings being painted white, as opposed to their current (non-white) colour.

For the first example, I'd say instead: "This tactic would be impractical due to the fact that schools have never implemented it." (The way it was written initially would certainly be understood, but would sound a little odd and stilted.) For the second: "Were all buildings painted white, residents would feel scared." This sentence would certainly be understood, and sounds more natural than the first example. But most people would probably say "If all the the buildings were painted white, residents would feel scared".