No design is perfect. For example, the current United boarding pass does not anywhere print the name of your class of service! If you're trying to access a Lufthansa lounge with a UA business-class boarding pass, you will have some trouble as agents squint looking for the word "business" or "first" somewhere on your boarding pass (it appears nowhere) and grudgingly accept that the flight number has a letter after it which indicates either the fare class (if printed at a kiosk) or the cabin class (if printed by an agent).

So, a UA boarding pass may say "930D" meaning that it's for flight UA930 booked into a discount business class fare (D fare), or "930J" meaning that it's for flight UA930 booked into the business class cabin (J), but nowhere on the boarding pass will it say "Business". I've heard stories of people who are only allowed into a LH first-class lounge when the agents, unable to prove that a boarding pass is really for the F cabin, finally give up and decide that the seat assignment "1A" must be first class.

So, no design is perfect. As everywhere this is an area where you need a deep understanding of what the product is for in order to design a useful product.

One obvious example of something that is missing here because of a lack of deep understanding of how air travel works is the ticket number itself, i.e. a reference to the actual underlying travel document which lets someone travel. You don't need this number immediately (passenger full name and flight number should usually be enough), but it can help a LOT with ancillary systems (online checkin, frequent-flyer mileage credit, etc.) Whenever I make travel arrangements, I always want to know my ticket number, which is strong evidence that I really have bought the trip (and don't just have a "reservation" that can be partially or improperly ticketed).

I'm willing to accept that maybe it was a deliberate choice in this design to abandon the record locator (the six-character code, sometimes called a "PNR", that uniquely identifies a traveler's itinerary from a particular operating carrier's point of view), but abandoning the ticket number seems a bit too much.

For a deeper example, the design in this blog post includes a "stub" which shows you where you're sitting (great) but does not include your date of travel (uh oh). If a gate agent rips off the stub and keeps the "big" part of your boarding pass, you will know where to sit (great) but may have trouble getting retroactive credit for your flight if your miles fail to post (because there is no date of travel on your boarding pass, which may make it harder to recognize and certainly makes it harder for you to remember which date of travel to look for).

(The "stub" in this design does have a barcode, but this almost certainly wouldn't be good enough for retroactive mileage credit. On a legacy carrier, there are something like 15 different mileage programs you can possibly credit your flight to, all with different rules and knowledge about how other carriers work. To get retroactive mileage credit on a flight you would almost certainly want the traveler name, flight number, date of travel, ticket number, and (if you can get it) carrier's class of service.)