All of ths back and forward on 380 v 747 goes to tell me is thet obvious - we're all different and we have different preferences and for very different reasons. And like opions they're all valid because they're ours and how we personally feel.. and also like opinions, there's no right answer.
That's also an opinion
To get back to should the P1 SST contact customers or be "proactive" during an aircraft sub IN THE CASE of pax is in Y on the same flight as scheduled, just the a/c type has changed? I think that's highly debatable. I'd also wager that, to QF, in the priority of pax to look after would be your paid F pax first, then your status, then your J's and so on. A P1 in Y, probably not so much. Right or wrong, the fare probably has something to do with the calculations, specially since to most people a Y seat at the date and time is a Y seat. Again, I am not trying to make a value judgement here - as above everyone has their own foibles.
Probably more important is the seating implications. eg if I was in an exit row and got subbed to a non exit row then I think I'd be more than entitled to be pissed off. Even a non exit but preferred seat that disappeared during a sub .. absolutely. However in a situation like this there is probably only so much anyone can do to satisfy everyone. eg shadows being there, then going, and a "friend" appearing in the seat next to you etc.
Remember the airline's priority is to get the people that booked that flight at that time to their destination as close to on time as possible (and hey the 744 will be faster than the 380 on the route

) and safely. If another flight cancelled and everyone was shoved in like sardines, well you know cough happens. Now, I could then say well if the P1 wants out and can be flexible to say move to the next day or day after to the 380 or some other routing, then sure make that happen I think - I'd say that loyalty has deserved some ability to make that kind of thing happen. However most people probably can't change on a whim and would rather get there. Well that shadow went away because joe bloggs had to get there too. In irops like this really all the usual rules and niceties would tend to go out the window as the focus is to get all those pax to LAX (and onward for some) on time.
my bottom line on this is it's an irops situation. Could QF have done better? Absolutely. Have they "wronged" the OP? I don't think so given technically he's been given what he paid for (a Y seat SYD-LAX on QF11 25AUG). Should the SST have contacted him and offered options? open to debate. Possibly, specially if his preferences were known, but I also am not going to jump on QF for not doing anything. I know any number of people (both non-FF and FF) who could care less what sort of aircraft it was they were on and would care more if they get the in seat TV and the like. People on AFF (and similar forums) are a subset of travellers who, in the main, do care and understand the various differences and even then some care to a greater or lesser degree (I mean if I'm in J, for example, on the 744 vs the 380, the only reason I'd potentially want the 380 is for a chance at the F cabin/service, otherwise the seats are the same sort and the 744 is the queen of the sky and a classic and I always love being on one). That's me. others are different. Storm in a teacup imho. A "fail" in terms of meeting the OP's expectations, but not really in other ways. In my view anyway (no offence intended)