Yes, it would be great if we could an official Drivers License ID app from the DMV that (like TSA Pre-Check) would work equally to a physical ID.
Maybe some of those Techies could work on that.
I'm not convinced that I'll ever completely ditch my wallet. There are still many cash only places; I was at farmers market this morning and 90% of the stands are cash only.
Also, you are SOL if you exclusively rely on your phone and the battery dies. No ID, no payment options. I'd still keep a physical ID and at least some cash on me.
Also, in the unlikely event of some sort of medical mishap or accident, having a physical ID may help first responders identify you quicker than trying to find/unlock your phone to find out who you are. If you have a subway car full of passengers and it derails, injuring many, if everyone is holding onto phones which get flung across the car, how quickly do you think it will take to match phones (assuming they aren't damaged) with the individual?
We don't live in a perfect world where a digital ID would be reliable. The best way of doing this would actually be an implant (like they do with some pets), but again might not be the quickest way for any random person to identify who you are (you'd still need the right equipment plus a network connection).
Remember, cellular circuits were overloaded after the Christchurch earthquake in New Zealand and authorities were begging people not to use their cellphone phones except for dire emergencies. Do you want to rely on exclusively digital ID and digital payment on your smartphone in those sort of situations? I wouldn't.