Ralph Breaks the Internet gets very meta. Within the movie's own lore, Disney exists, as do the characters from Disney movies and Pixar movies. Moana is featured and recognized as a Disney character, which means Ralph Breaks the Internet takes place sometime after 2016.
Could that mean Wreck-It Ralph, the 2012 film, also exists in the universe of its own sequel? Could Ralph go onto the internet and find references to his previous movie?
Yes, it is entirely possible that the 2012 Wreck-It Ralph film exists in the Wreck-It Ralph universe, although admittedly it is never explicitly mentioned.
Unfortunately I don't think there is any single piece of hard evidence that proves it. However, I offer this conclusion based on solid reasoning that considers several well established in-universe ideas. I also considered the points you have made in your answer against the film existing in universe and I offer explanation of them as well, not as a slight against yourself, but simply to try and strengthen your belief in the possibility of the film existing.
Here is my reasoning:
We know that Ralph et al already know of a world outside of their own; they are aware of the arcade, they know of the players, and they know that these people are able to do things that they themselves cannot (for example, unplug games). So the idea of an unknown 3rd party making a film all about the life and times of Wreck-It Ralph wouldn't be a completely alien concept to them. They may still be surprised to find 'the players' are interested enough in their lives to go to such lengths but it still wouldn't be a huge revelation ala The Truman Show.
They have Wikipedia, Facebook and YouTube. Since Ralph et al are new to the internet they probably aren't aware of this for the duration of the film, but after just a little time exploring on-line the concept of User Generated Content would be known to them. It isn't clear from either film exactly how much 'the video game characters' know about how much influence 'the players' have over their world. They know it is based on 'the code' but do they know that people outside of their world wrote the code? I'm not sure. Opening their mind to User Generated Content gives them the concept that 'the players' can generate stuff of their own. Knowing this, I believe Ralph could then accept that a film of his adventures could exist in universe.
Presuming the film universe is very much a mirror of our own with a couple of fictional elements, it is probably safe to assume they have Twitch. (For those that don't know Twitch is an online streaming service geared towards sharing videos of people playing video games (although it has started branching out into other areas)). This would further back the idea of a film of Ralph's adventures being possible, the idea that players have a way to capture moments from their games to playback and view again later as videos. Ok, this argument would need further 'finessing' to explain how a game streaming service would capture out-of-game events, but a simple explanation would be that those moments are in-universe CGI.
We have precedent from another Disney film! Toy Story! In Toy Story the main character, Woody, is featured as the main character in the in-universe TV show Woody's Roundup, yet he knows nothing about it until told by another toy in the second film. Given that Ralph et al live in a rather closed society (until the introduction of the internet) it is perfectly reasonable to assume no-one in their circle is aware of the film and hence it goes unmentioned to him so he never knows about it.
Continuing to use Toy Story for my next thought (which addresses your thoughts), in Toy Story no-one refers to Woody as the character from the hit TV series, we (the viewer) don't even know he was in a TV series until the sequel, and this is an in film, definitely-exists-and-is-known-of-by-some-of-the-characters TV series. You could argue that in the first film this in-universe show hadn't been established so couldn't have been mentioned, but come the third film it has been and yet still no-one mentions it. It is only mentioned when they are actually talking about the show. So to me the argument that no-one refers to him as the character from the film doesn't really support the view that it doesn't exist, given that the same thing happens here.
Even without the Toy Story precedent, if I was to mention to you Ken and Ryu where are you more likely to know them from? The 1999 animated movie Street Fighter Alpha or the 1991 video game Street Fighter 2? What about Mario and Luigi? The 1985 video game Super Mario Bros or the 1993 adventure film Super Mario Bros? It's not huge leap to assume 'the players' know and refer to Ralph as the guy from the video game even when the film exists because that is what he is best known for! Even further, perhaps in-universe the film tanked and no-one knows about it other than the gamer geeks and nerds! I could imagine why, consider how different the film is compared to the game it is based on!
So in conclusion, yes, a film of Ralph's adventure could exist in universe. There is no strong evidence to suggest it cannot but plenty of circumstantial evidence to suggest it could.
The "Wreck-It Ralph" arcade game is fictional, but in the Wreck-It Ralph movie's canon, it is a well-known game. There are also fictional websites e.g. BuzzzTube. So this universe already has some fictional canon, even though much of it is based on our own.
In Ralph Breaks the Internet, when
internet users react to Ralph becoming a viral meme
they refer to him as a character from an old arcade game. They don't refer to him as the character from a 2012 Disney movie. So it's possible that in the movie's universe, the 2012 Wreck-It Ralph film didn't happen.
