Interesting idea

How would opening theory and middlegames change? The evaluation here is the same as the normal starting position.

It’ll be weird as hell 

idk

maybe people will still do similar openins

the problem is after e4/e5 black can't play b5/b4

would you still be able to castle and play en passant?

very weird, there would be much more early contact and crazy play

the back rows could be used for hiding the king or rerouting pieces

yeah

A game played by the analysis engine:

Like icy said, the back ranks were used a lot in rerouting the pieces

But the queens were traded instead of the kings hiding, without castling it may be a bit tricky

endgame is god

I've played like that before