In displacement Chess, the king and queen of one side is interchanged. Game exactly as in chess except for castling rules.

Allow flexible castling which allows King to move one to three steps towards rook instead of just two. E.g. white can here castle (if no pieces in between)by moving king 3 spaces towards rook on b1 and rook next to king on c1.

White can also castle by moving king to d1 and rook on a1 to e1.

What do you guys think about this variation. Opening theory is out !

The flexible castling sounds pretty interesting.  I'd have to play a few games like this to see how it went.  It's close enough to regular chess though that I almost feel like asking "what's the point?"  It's also worth noting that the position is really just one position out of many of chess960 or Fischer Random.