I agree, the unit ends have to be painted anyway so it might as well be yellow, which could be useful in some circumstances.But people make mistakes sometimes. Anything that can mitigate against mistakes (or their potential consequences), should attract consideration at least.
Thailand doing it to all coaches is interesting, but obviously it won't work for freight vehicles, but still "every little helps!"
@Sorcerer makes a good point that an unbiased review would be worth doing - although I think I would use that to decide whether a campaign was justified (at some cost) rather than just changing the rules and converting to yellow ends as maintenance/overhauls proceed.