That's a pretty weird example, because that is the _only_ stock that trades at $200,000/share. Such a high price forces away liquidity intentionally, because the capital requirements of even 1 share are larger than most futures contracts. For most individuals it is more like buying a house than a stock! As a result, there is a NYSE employee (I forget the title, maybe DMM?) on the floor which _manually_ matches buyers against sellers. Other exchanges I believe still match electronically.
Aside from that, how does your statement relate to inventory risk? Market makers and grocery stores take on inventory risk. An absence of market makers in BRK.A* would only show that nobody wants to take on that risk. It does not change the role of the exchange. Exchanges facilitate matches, they are not a counterparty.
