Is there a playstyle of chess where both players agree to skip the opening, just setting up the board as if the opening were played "by the book" by both players and going from there? It seems like that'd be much better for getting amateur-level players practice in their middlegames, since they wouldn't need to worry about perfecting the opening before they could even attempt it.
This type of training game is more often used to practice a certain structure that arises from a specific opening, and thus is a type of practice used more towards the higher levels of play (International Master+).
The thing is, if two amateurs are playing, neither of whom deeply know openings, then the starting position (or 4-5 moves in) is essentially new territory, like what might arise for a Grandmaster 15-30 moves into the game. Does this make sense?
The slight variations in the opening tend to be important to the middlegame that follows. You can set up the pieces 8 moves into mainline Ruy Lopez, for example, but if you start from exactly that position every time then you just end up with a "second opening" after that point. Randomizing the start position is possible but undermines the whole "pure battle of intelligence, no chance involved" shtick that is part of chess' appeal.
Fundamentally with the exponential fanout of the moves but a relatively small set of choices initially, there's always going to be a point where the game transitions from "likely to be an exact position I've seen before" to "likely to be something new, but similar to previous games".
I don't know of human games that do this (except for practice), but this is done in computer games. See the Thoresen Chess Engine Competition (TCEC) where the first 8 moves for both sides are played by the book and then the engines take over. This is good as it ensures the engines are tested over a wide variety of positions.
