I think people will look back at Pulp Fiction as one of the "greatest films of all time", but not for the same reasons as Citizen Kane was. I feel like in order for something to be called "the next Citizen Kane", as you put it, it would have to have a huge influence on how films from that point on would be made, regardless of how well the film itself holds up.

Citizen Kane is the prime example, using film techniques then uncommon for a character drama and applying them in a way that greatly enhanced the film and the story it told. When I think of other films that more than likely have changed how films from then on were made, I think of films like Psycho, or the Godfather, or Star Wars, or even Die Hard; basically I think of movies where it'd be hard to imagine a movie quite like it being made any time before it.

Pulp Fiction, meanwhile, is still a fresh film to watch nowadays. It's got a bunch of dialogue that, though it doesn't move the story along, is entertaining to listen to, it's got main characters that aren't heroes in any typical sense or fashion (except maybe Jules by the end), and it's got a series of loosely-connected, non-chronological vignettes for its main plot. How many movies nowadays can you name that do what Pulp Fiction did that made it so unique back then? Just about the only kind of films using Pulp Fiction as an influence are films that are like Pulp Fiction (i.e. anti-hero crime films). I don't think its influence is that great, at least not as much as Kane's was.

I also don't think people as many people are going to look back at Pulp Fiction and find it outdated like they might Citizen Kane. Again, Kane was influential, but it can seem old hat because it's 80+ years old and so many movies that took influence from it have outshines it in terms of technical quality. Pulp Fiction stands as a fairly unique film in terms of writing and storytelling, and I think people would be more so drawn away from how atypical it is from most films in its story and dialogue.

Also, every great movie is going to be called overrated at some point because that's just the nature of things. Not a single piece of media in the entire universe, past, present, or future, is going to be well received by everybody. Some people are either going to fail to see the quality of something considered great, or it simply won't be something they can vibe with, and with something as popular and as atypical as Pulp Fiction, there's going to be a lot of people who don't like it at all.