Previous BBC Who releases tended to put lengthy extras on a second disc. (It’s also possible the animation and the telesnap version are easier to compress than a regular restored story, but that’s still nearly five hours in total.) I’m only watching the colorized version with the commentary switched on out of curiosity. The UK version doesn’t seem to have the second color disc at all.
Widescreen seems to go against the grain of recreating a 1960’s tv show, but they don’t have to blend in with any vintage material, unless an 16mm reel or two magically turns up in the near future. 😉