His version of One More Day would have the past being changed going back to Amazing Spider-Man #96-98 when Harry Osborn was hooked on drugs. The change would have Peter helping Harry out, which led to Norman not killing Gwen, and with Gwen alive, Peter never married MJ. JMS's main complaint about OMD is that it did not detail what caused Peter and MJ to not marry. He didn't have any problem with the deal with Mephisto or even ending the marriage. But when people complain, he says that editorial changed his original story.
On Sins Past, he wanted Peter to be the father of Gwen's children. He also thought that the story would by retconned by OMD along with the marriage. Editorial nixed the idea of Peter being the father and suggested Norman instead. JMS went ahead with this version, but when it was criticized, he again said that editorial changed his plans.
The problem I have with this is that even if Marvel went ahead with the original version, the story would still be bad.