The promised land was said to be a myth by the Doctor. Yet it turned out to be a place (of sorts). And a piece of Timelord technology. Could it be that the "Promised Land" is actually Gallifrey. Just that the myth is actually the one the Doctor is looking for and the Master is denying him.
In "Robin of Sherwood", the navigation screen for the robot's ship states the destination is "The Promised Land". For this to work, a celestial location needs coordinates. So, by the third episode, "The Promised Land" is a fixed location in space, with its coordinates in a navigation databank.
Technically, it is a fixed location, the Nethersphere. However if that happens to be unside Missy's TARDIS (one assumes she has one), it could go anywhere in time and space. It is also possible that the Nethersphere was not the promised land the robots were searching for....they could be looking for a planet lost to time and legend. A planet known, as Gallifrey.
Perhaps I missed it.... was it established in an interview somewhere that the writing of the arc was changed or have the fans come to this conclusion?
No, there is no evidence the arc were changed. Even if it were, it wouldn't be evident in the finished product since Moffat likely had the arc mapped out before anything was even written. Like he did with all his previous seasons, and RTD did with his seasons.
Moffat also seems to have Doctor arcs as well as season arcs. It might all be made up over time, but things that happened in Matt Smith's first episode come back around in his last episode with things all along the way shaping how things went and how things were going to happen. Perhaps some of the "Promised Land" part is for later in Capaldi's run.
Kinda like how Season Five revolved around the Tardis exploding, something that wasn't resolved until a throwaway line in Matt Smith's final episode four years later
Yeah, that was kind of annoying in Time of the Doctor where we basically get some of the biggest questions from the Smith era just hand waved away with a few lines of dialogue. "The Silence are actually good guys, but the ones you encountered were a renegade faction in league with Madame Kovarian. They destroyed the TARDIS." "Very good, anything else I should know?" "I'm a Dalek."
I always figured that was because Moffat had to clear the decks for Capaldi when he'd planned to answer those questions over the course of S8 with Matt Smith... Maybe?
Good: Deep Breath Time Heist Mummy on the Orient Express Dark Water Meh: Robots of Sherwood Flatline Death in Heaven Bad: Listen The Caretaker Kill the Moon The Forest of the Night