Royal Piece Swapping places with another piece

One special rule I read about for the ancient form of chess known as Tamerlane Chess, which predated modern standard International Chess by a few hundred years, was the ability of the King to switch places with a non royal piece while in check.

I think it could be interesting to have this as an option for a special rule in custom variants.

It would mean that in this position for instance, assuming white didn't play the switch previously, white would not be in checkmate as all of the non royal pieces would be on safe squares so white could play a move that results in a position like this

How bout the "royals cannot face each other" as in xiangqi and Janggi?

@Lewis0428 that would be pretty cool, and also if the royals could be confined to a 3 by 3 box, without using walls like in Xiangqi.

Edit your board since in the first Position, White can just play Qxf2

Thanks for pointing that out @ChessPawn921, I fixed it so that the piece swap would be the only way out of check, so that without the piece swap allowed it would indeed be checkmate.