I had a recent experience that may relate to this thread. An early morning arrival into a large but isolated regional airport. The forecast indicated not more than SCT cloud below alternate minima (WX, tick), flight was due to arrive more than 10 min after first light (lighting, tick), sufficient navaids (navaids, tick) = no alternate required, but a little extra fuel was carried. Check for updated forecast enroute, no change. Getting close to destination ask for latest METAR, advised that a SPECI had just been issued with cloud BKN004 (below alternate AND landing minima). New TAF issued two minutes later with BKN005 (below landing minima) to remain until a couple of hours after the arrival time.
If the flight proceeded to the destination on a hunch that a landing could be made with fixed reserves intact then maybe nobody would hear about it. However, if the flight proceeded to the destination then couldn't get visual and then subsequently declared a fuel emergency with a descent below minima to land I am sure the PIC would be asked some serious questions... In my view, it would be irresponsible to 'commit' to the destination when you now know that an alternate is not only required but almost certainly would end up being the place of landing given the slim chances of getting visual when the cloud is BKN well below landing minima. I would like to see the rule that effectively states that 'pre-flight alternate considerations can be ignored inflight' - I think I will be waiting a long time to see a reference...
With the accuracy (or lack thereof) of weather forecasts lately these 'hypothetical' situations may become more practical than we would like. Makes for good discussion!