Update: Apparently there's a company called Ruumr who is doing this.
Problem: We lost out on the opportunity to offer a winning bid on a house we loved because we had no idea how much the winning bid was. Maybe it was for $15K over and maybe we would have bid $16K over! We have no idea. It doesn't matter now because we never got the chance to counter offer. Which, in a twist of irony, means the seller lost out on a bidding war that almost certainly would've resulted in a higher price.
This idea of blind bidding - guessing what the others MIGHT offer and attempting to bid over that amount - is a ridiculous, antiquated idea.
A bidding platform would be incredible, not only for the sellers who potentially make more money, but primarily for the buyers who can see competing bids in real time.