There's no evidence for it. Hey, here's my theory for the walking dead. It's all Rick's nightmare! Why do I think this? Well, it's awfully coincidental that he went into the hospital after being shot and then just suddenly started seeing everyone around him die! It's clear that it's all in his head, he's actually lying in that hospital bed and is gonna wake up any day now.
There needs to be some indication that it's not reality. Think about the movie Inception. You can call into question whether the end scene was reality or not based on the spinning top. In fact, the entire premise of that movie was questioning the line between reality and dream, so it's clearly something that can be argued.
There was no such subtext at all, ANYWHERE, in Breaking Bad. In fact, the one of the main themes of the show was quite the opposite.... that reality is absolutely what we see, what we feel, what we can experience with observation and what can be tested and verified.
Furthermore, other than the ending seemed to "wrap up too nicely in Walt's favor," there is no evidence on the film that it was a product of his imagination either. It's not like it's some crazy stretch of the imagination that he could find an abandoned car. Was it kind of a cop out to have him find the keys in the overhead sun blocker? Sure, but that's not evidence that Gilligan intended it to be a hallucination.
If it was a hallucination up in the cabin, and he died in the cabin after dying on the floor of Uncle Jack's meth lab in his dream, where are the on-screen indicators that this is the case? Gilligan would have left some sort of clue, like, the floor of the meth lab is the same floor pattern of the floor in the cabin. Or the last scene we see of Walt in the cabin, the clock reads 2:04, and that is the exact same time it was when he's lying on the floor in the meth lab at the end. Something like that.
You'd leave clues. You'd drop hints that it is what you mean.
There's nothing for that for Breaking Bad. Just rebellion to the idea that Walter White was able to wrap things up so nicely for himself. But that's not really good enough IMO.