Oh absolutely, just 1 or 2 moves would be more than enough to really shake things up and make players far more defensive. Three moves are generally crushing an

Oh absolutely, just 1 or 2 moves would be more than enough to really shake things up and make players far more defensive. Three moves are generally crushing and four is totally unplayable. There aren't many positions where four moves for your opponent won't get you checkmated. There is general chess advice of "Give you opponent three free moves, what would they do?" But even that advice implies those moves would be sensible moves, i.e. not just hang pieces in the intermediate moves. Perhaps if pieces couldn't move en-prise in the intermediate moves it would be improved but I think 3 or 4 moves would still be crushing. Even a single tempo loss is a big concession, to the point where in some opening lines players will happily sacrifice a pawn to be a tempo up with a good attack (e.g. Smith-Morra). It feels like there are missing rules about not being able to capture in intermediate moves (or a capture ending the whole turn). Given 4 moves a queen could trivially capture three enemy pawns/pieces then move to a safe square. Even just capturing two pieces and moving to safety would be a decisive advantage.