I think you could account for hold-out by having the resolve window be longer than the trade-insert window, at least to an extent.

The trade-insert window can't be too long, or it would leave lots of room for regret, like people who voted by mail for a candidate caught in a scandal two days before an election.

why should randomization be clever? just fulfill orders in the book randomly for each time interval, wouldn't that be enough?

If I place an order to buy 1 share for $1 and another share for $1.01 because the market data shows that there is only one share available for $1, then the exchange needs to process my $1 order before my $1.01 order. More complicated scenarios exist, too, especially once you take into account resting orders and modifications to existing resting orders.

Right, unless exchange explicitly documents the fact that order of fulfillment is not guaranteed if you place them within the same time interval.