This is actually a really interesting question. They would have to show size at the inside otherwise sweeping under Reg NMS would be impossible (you have no way of knowing how many shares to clear the protected quote). Also they already have a prop feed (IEX TOPS) that already shows size/price at the inside.

Under their proposed Rule 11.330, they only have two prop feeds which are the TOPS feed and a last sale feed. So no full depth feed. They would be the only US equities exchange without a full depth feed, but it looks like that's what they want to do.