That just seems... bad. Also easy to circumvent by moving along diagonals. You can even zig-zag your move so you can wind up where you want. I could go E6-D5-C

That just seems... bad. Also easy to circumvent by moving along diagonals. You can even zig-zag your move so you can wind up where you want. I could go E6-D5-C4-D3-E2, then you couldn't en passant to E3. Not that you could do it on E3 as that would put you in check and isn't allowed. But G4 to E4 is a legal move with the same outcome in your scenario. I really can't see a way that you'd be able to en passant a king that's not easily routed around or just illegal. It also violates the concept that you're taking multiple turns. You can capture a pawn en passant because the pawn's double move is a relatively recent rule. It's solely to make sure you can't avoid capture by using the double move. But it's still a single turn. The die roll lets you move that many pieces. As N distinct turns. If the turns would have played out one-by-one, it wouldn't be allowed as a player can't put their own king in check, and even if they were allowed, the opposing player could just take the king in response. And it's no longer "in passing" if it's from several columns away.