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What exactly is this supposed to add to the game compared to orthodox castling? It seems to me it would be strategcally foolish not to castle to a square one step away from the corner. Standing in the corner is in general a weakness, as your King defends one less Pawn, and has fewer escape squares. Standing further away from the corner leaves a gaping hole n the undefensible side of the King. If in a certain position it is not allowed to castle the maximum distance, because you would castle through check, it would be suicidal to castle in that direction in the first place.

So the only application I see of a variable King destination is that in Q-side castling one now will always go to b1/b8 in stead of c1/c8. But to get that, the much simpler symmetric castling rules as in Janus Chess would suffice.

The variable Rook destination might have some use, although this is largely spoiled by the fact that we are not allowed to give check. (After all, this would be the main reason why you need the Rook immediately in a certain position, rather than allowing an extra move for it.) Usually castling is done in a game stage where there are no open files yet, so the position of the Rook is rather indifferent. So why not put it always next to the King?

It seems to me that this adds very little to Chess, other than complexity we could do without.