Yes, that’s very true! In Australia……that’s not the case if you venture beyond our borders. Elsewhere, Atis and metar do have a NOSIG or trend attached that you can use for planning. I understand that this is not practical in the Pilbara as you would need someone there to forecast but ‘TAF 3’? Keep it simple and have a metar with a trend attached….why do we have to be Oztranauts?
A TREND or METAR with trend attached is basically just what we call a TTF or now a TAF3, with a shorter useful period of 2 hours instead of 3. As you already know having TREND requires a MET observer so it's not going to happen outside of places that already have TAF3 so it's really irrelevant, and the TAF3 offers better coverage anyway. If mine sites wish to pay for a met observer to sit and watch clouds, fair enough, get them approved to issue TAF3s. But without any benefit form it such as lower minima for CAT 1+ and so on, it wont have any safety implications and the trend can always be wrong as much as any TAF. It can just be more rapidly amended, which means nothing if you are already en-route nearing destination when it happens.