That’s an interesting way of putting it. I dunno if I’d call it “conservative” but rather anti-radical and stolidly centrist (spoiler-block as to why below), and certainly almost entirely uncritical of capitalism. Oddly the worst offender for this, for my money, isn’t any of the Iron Man movies but rather the most recent released Spiderman movie, which rather crudely and ineptly strawmans anti-capitalist, anti-corporate sentiment and tries to make Tony Stark (of all fucking people) into a sort of wise, paternal figure (?!!?!? - next up, Snake Plissken teaches you how to knit baby booties). Even the criticism of the military-industrial complex has largely been of the “Well some arms companies are bad but some are okay!” Not-all-Arms-Companies bullshit kind.
What they do next will be very interesting. With Wakanda, specifically, they will potentially say a lot, whether they mean to or not. If it’s portrayed as a basically capitalist utopia (which would make absolutely no sense on a basic economic level note - it couldn’t have had any real trade due to being cut off from the outside world - closed systems that have reached their limit of expansion cannot be capitalist, it’s just not economically possible - they inevitably controlled economies with light faux-capitalism for bottom-level redistribution efficiency), whereas if it’s portrayed as something more Star Trek, something post-capitalist, and is really looking to help the entire world (and not with loans or paternalism), that’s a bit more modern and less lazy.
Quite and as climate change and other crises bite, or even just loom larger and larger in the public consciousness (which climate change is currently doing), I don’t think it will work to make movies that completely ignore that kind of thing. Movies where the threat is purely external and can simply be thumped or tricked. I think they’ll have to look at doing something which has a bit more going on, which is more about necessary change. I doubt we’ll see anything riskily progressive but that’s a message you could have and bring the vast majority of your audience with you.
I do think it will seem preposterous eventually, I’m just not sure it’ll happen that fast, because it’s not sufficiently clumsy. It’s not Cobra, y’know? That was a film that was almost understandable in a sort of ridiculous paranoid way in say, 1986, at least to some people, but was laughably ludicrous by even 1992/3 when I saw it. Red Dawn likewise, and quite a few others. It’s also a lot friendlier than those movies. There’s nothing really in Endgame which seems mean-spirited, which some might argue is a form of weakness, but means it’s less likely to trigger the sort of critical examination you’re looking for. Plus some movies go the other way. Cobra and Red Dawn and the like are seen as ridiculous cultural artefacts, ludicrous things preserved for us to laugh at. But look at say, the Dirty Harry movies. The critical reception at the time was almost aggressively hostile with terms like “fascist” being tossed around by a number of major critics (very inaccurately, I should note, but that’s another discussion). Later critical appraisal is actually lot less hostile, even in this far more liberal and human-rights-oriented time.
I think the whole “Really, they were into that?!” thing will come later. The Marvel movie thing of the twenty-teens may be seen like one of the crazes of the twenties or thirties. If Marvel fucks it up by simply trying to repeat the process, rather than evolving it, that’ll definitely happen in fact. There was some completely berserk one I read about from the 1930s a while back, trying but failing to remember what it was.
Also re: ten-twenty years, that will be how long it is before people who grew up with this stuff are actually the people writing and directing (and to a lesser extent producing and commissioning) movies. So that’s when we’ll see the real responses to this. I’m sure you’re right that some expert critic will totally deconstruct Endgame and the whole Marvel phenomenon in a brutal and accurate way in a few years, even sooner - but the influence of that will be absolutely minimal. Film students might come across it, no-one else. But filmic responses to it, which may well critique it in a way that has a broader cultural impact - they’ll take a while because of way society works.
I think perhaps the first thing that’s going to get criticised, and I’m surprised it hasn’t been more of an issue already, is the lack of LGBTQ characters. I’m sure some people reading this are rolling their eyes, but it actually seems a bit weird at this point, especially as so many of the characters challenge societal norms in various other ways.
EDIT - A key thing for the future of Marvel’s movies I think is really what they do now they have the X-Men franchise and so on back - it’s potentially a good vehicle to chart a different course, if they want to do that. I think they need to ignore the Fantastic Four, though, or completely, on a very basic level, have a new take on them, because they are literally, and Stan Lee almost said as much, a conceptual parody of 1960s gender issues (Mr Fantastic, The Invisible Woman, The “Rock-Hard” Thing (which he has been called many times), and The Human Torch for god’s sake, it’s right there in the names!). That shit just can’t fly any more, and no, making the Human Torch or The Thing into a black guy does not improve matters. Arguably it makes them worse. If they do a very canon take on the FF, I think that will sell tickets initially (not to me, admittedly), but I don’t think it will work in the longer-term. It’s too deep-Boomer. It’s hard to find a serious FF fan much under 50, and most are more like 60-something. Anyway, X-Men yes, FF no, or not without massive revision.
I wouldn’t necessarily call the whole MCU really “conservative”, except in the sense that it’s not really “progressive”, certainly wouldn’t call Endgame that, because it doesn’t have a true reset button, they actually emphasize that you can’t turn back time, you must accept what has happened and try to make the best future - which is a directly anti-conservative statement. That’s saying the central tenet of conservatism, which really is “Let’s go back to the good old days!” however it’s packaged, is basically false, much as Rees Mogg wants to Back to the Future us to Victorian Values or whatever.