[T]he idea that 5 mins out and fuel for 30 mins holding at dest requires a "min fuel" call, but that magically becomes an emergency when the computer ticks over and shows only 29 mins ... it might need a mayday but no way is it impending doom and an emergency.
And that’s why it doesn’t make sense to mandate a mayday in that scenario.
In the situation where you ended up landing and happened to have 29 minutes of fuel remaining at the specified burn rate on a beautiful cavok day and happened to be ramp checked, I would seriously hope the person doing the check would have the discretion to let you off with a stern warning in the same way a police officer who is compelled to enforce the road rules might use discretion and let you off with a warning for a burned out brake light.
Of course they have discretion.
But why should
that scenario be a breach of the law in the first place? A breach of the law is a breach of the law and, although you might get ‘let off’ by the FOI, your breach will be noted in CASA records.
I should say I never plan to, and rarely land with, less than 45 minutes of legally useable reserve calculated at a conservative rate. However, if ever I got into a situation in which I’d stuffed up or there was a much bigger headwind than forecast and I calculated that I’d land with e.g. 20 minutes of legally useable fuel, I wouldn’t consider it an emergency provided I was sure of the weather and runway availability at the destination. There’s about 20 minutes of useable ‘legally unusable’ fuel on the aircraft I usually fly. I know this, because I’ve used it.