Fascinating post, Davina!  I'd never thought of it like that (ie, as deeply) but what you say makes a lot of sense.  Thanks for raising these ideas.

Taking the image of Moriarty on the throne a bit further:  By sitting there, he is not just a king; I would posit that it makes him emperor.  To me, as an American, the Crown Jewels symbolize Britain's (former) power as an Empire.  Encapsulated in the regalia of the monarch and sitting on the throne at the symbolic center of British power, Moriarty is showing everyone that not only is he at the pinnacle of personal power, he also controls his own empire--that of criminal enterprise.  He is flaunting his power to the Establishment by smashing the glass that protects the symbols and then wearing them as his own.  And if he strike at the very heart of Britain with impunity, what else is he capable of???  He's like a little boy sticking his tongue out and saying, "Nah, nah, nah, nah, nah, nah!"

I see some chess pieces being mentioned in TRF:

King (King Arthur/"...the man with the key is king")
Queen (represented by the crown jewels)
Rook (= Rich Brook)
Knight ("the knights of the round table")

hmm... bishop...pawn...(where are you hiding?)

interesting, Davina!

Oh, absolutely, the chess metaphor works!  For me, anyway.  Sherlock is white, Moriarty is black.  White as a force for good--and aren't angels usually clothed in white?  Black denoting the bad guy--in Westerns, the bad guys wear black hats.  Though in some Asian cultures, white is the color of death, which also seems somehow appropriate here...  So Sherlock and Moriarty as kings on opposite sides of the giant chessboard that is London--all those street grids--and the world: Yes.

Using people as pawns: Definitely.  Moriarty uses the innocent hostages in TGG--could there ever be a more classic example of a pawn?  Sherlock, as you said, Davina, also uses people to get what he wants.  And, btw, Mycroft treats people as pawns, too: Witness how he interacts with John.

Moriarty believed that he'd checkmated Sherlock in TRF but he was wrong.  The game is sort of at a stalemate, in that Sherlock has to lay low for a while but he will, in the end, prevail and will, undoubtedly, make a surprise move that will catch his opponents off guard.  In the meantime, John seems to be at a stalemate in his life as are we, the audience, in terms of what to do without having Sherlock around. 

They do have a chess board at Baker Street too.

Sherlock and Moriarty have a chess game together in the RDJ movies, so it's obviously a theme that people like.

Well spotted BigFan!

The two 'Knight' bookends turn 90 degrees during that scene (Continuity error?).

I'm unsure as to whether there is a larger conspiracy related to chess and Sherlock/Moriarty noted by said bookends - but the original analogy stands well.

-m0r