The Hell Bent TARDIS was inspired by the original Hartnell desktop. Showrunner Steven Moffat visualised the Hartnell desktop as the "default" theme (think of the green hills Windows XP wallpaper). This TARDIS isn't accurate to the Hartnell desktop though, nor is it trying to be, but it's a very nice callback!
Notable discrepancies are:
- the Hell Bent set "footprint" is completely different (walls in different
layout and not aligned with the shape of the console)
- it's a 360-degree set, the 1960s set was missing the "fourth wall" as it's where the cameras usually were
- the server banks have been redesigned
- the viewscreen is a modern flatscreen TV not a 1960s television set
- the 1960s set was also painted a pastel green IRL to show up pure white on old B/W televisions
The parts that are accurate are the console itself, the roundels by the doors, and the hexagonal ceiling centrepiece over the console - all were reused pieces originally built for the docu-drama An Adventure in Space and Time (featuring a very accurate recreation of the Hartnell desktop) and were also displayed at the former Doctor Who Experience in Cardiff.
Another little easter egg, the wall with the backlit vertical slits is recycled from the Gallifreyan "extraction chamber" earlier in the episode!