There is 100% a subtext to John’s bedroom in 221B – we have not been show this room yet, and the times it is discussed or referenced are very suggestive. The first time it’s mentioned is when Mrs Hudson asks if they’ll be needing two bedrooms (asking whether they’re together). The only other time reference is made to John’s room is when Mrs Hudson calls up the stairs, “Boys, you’ve got another one!” after a client faints in the entry way. Easy to look over, but why would both John and Sherlock be upstairs in John’s room together …. ? Very suggestive. 

Sherlock also completely associates John with 221B – how happily Sherlock smiles when Mycroft says “Back to Baker Street” after he’s just been tortured, his shocked expression when Mycroft says John is no longer at 221B – Baker Street and John are one and the same to him. When Sherlock is stroking the wallpaper in his mind palace trying to come back to life (the last image that he sees before coming back to life in fact being 221B’s door), that’s about John. And in this way, you can view John’s bedroom as the highest level of 221B that is still to be ‘unlocked’. We’re definitely going to see John’s bedroom eventually and it’ll likely coincide with something else ~