Okay, so I just checked in for my flight and figured out what is going on.
They want people to use-- or present certain people with the opportunity to use-- their new "Digital ID".
It gives you a special place to drop off your bag:
You create your United Digital ID in the app by taking a selfie and scanning an ID. In my case, it didn't like my Illinois DL (after several attempts), so I tried my US Passport. Interestingly, after photographing your passport, you are asked to hold your phone up to the chip of your passport so your phone's NFR can read the biometric photo data from your passport, which it shows it is doing in a progress bar once it makes contact with your chip.
Here is how a United Digital ID looks in the app once it is done successfully:
You can use your Digital ID to drop bags, but it says you need to present a physical ID when dropping bags; I will report back, but I have no reason to assume that's not true. (And this might be that annoying micro-criticism that can't be dismissed-- see post #22). You can also use Digital ID to board domestic flights at enabled gates when it is being utilized (so my Apple Watch wallet is now obsolete).
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It would be interesting to know if those who got this Mile Play offer are departing this week from certain hubs (eg. ORD, like I am-- or another major hub like SFO, where the
trial was done last year).
It appears the structure of the incentive is to maximize the possible touchpoints that expose United customers to Digital ID, giving a smaller bonus for the less likely touchpoint (going to the app for exposure Digital ID and a chance to sign up + a chance to use the technology for boarding on certain flights), and a larger bonus for the more likely touchpoint (a chance to use the technology at bag drop on all flights at certain airports). The extra bonus appears to incentivize customers to hit the touchpoints most likely to generate use of the technology (going to the app for exposure Digital ID and a chance to sign up + a chance to use the technology at bag drop on all flights at certain airports).
What can I say; it worked: I am testing out Digital ID. (And of course I am certain to get a survey on it).