I've heard JDM complain as much in an interview, that he wants to come back to the show and put things right because he feels like the writing for John got really messed-up later on. It still confuses me as to why that never happened, especially when he still seems very friendly with both Jared and Jensen. I understand his schedule being busy, but you'd think they could have worked out a single episode appearance in the past 9/10 years

The impression I get was that the writers became very attached to the Bobby character, so writing him as surrogate dad, as well as not having JDM available for filming, all added up to John losing out every time when it come to the "Winchester Dad" comparisons

I wasn't the characters biggest fan, but he went out on a good note in season 2 IMO, and his last interaction with Dean was very positive and an attempt to make amends, so it is a shame how one-note the writing has become for him since then. Aside from appearances with younger John I guess