new variant idea

queens are also subject to check and checkmate. 

Queens can also castle both ways. Same castling rules apply.

When pawns promote to queen, that queen is also subject to check and checkmate.

what happens about the kings?

do the become unroyal?

both the king and the queen

can both the white queen and white king castle during each game?

yes 

can a royal queen check a royal king?

if a queen is checkmated, does it dissapear off of the board?

a queen can check a king.  If a queen is checkmated (which is very hard), that player loses the game.

queen legit becomes useless 

not really

but worth a little less than a rook imo

a queen can checkmate a king if it is far enough