I still think Arwel’s picture just shows two parts of the set randomly being placed next to each other without any further purpose. (The question is though, why they take down the set already). But what made Arwel choose the word “morphing”?
Maybe this would be giving away too much, but…
Most of us think, looking at the given clues, that ep 4.2 is an adaption of The Dying Detective. In this story Holmes locks himself in his bedroom. pretending to be seriously ill, and sends John to solve the case. We’ve seen Sherlock wandering through London, but he seemed a bit off. Somehow intoxicated, poisoned? I wondered, if he were halluzinating instead of deducing.
So maybe, what’s morphing is 221 B. Sherlock doesn’t lock himself physically in 221b this time, but he’s locked there inside his mind. Everywhere he goes, the real world starts morphing into 221B. He may be unable to talk to people, to see what’s going on. All he can see are the walls of 221b and he can’t get out.