I actually loved Norm's theory. I read it from another writer as well, and I had considered it myself. As someone else mentioned, there are a lot of moments in the finale in which Walt appeared "ghostly". Watching Walt Jr. through the glass. Talking with Skyler. Being able to park his car wherever he wanted inside the Nazi compound. The list goes on.
Vince gave viewers essentially the ending they wanted, and I loved it. I could watch the M60 scene over and over again, much like I could watch the pistol-whipping scene from Goodfellas over and over again (yeah, I know, I'm sick and I need help). But there were touches of the finale that felt 'off' ... and again, I am OK with that.