I agree that a big bonus of e-tickets is that you don't have to worry about losing an orange (other colours are available!) CCST (credit card sized ticket).I like them, they don't need a battery and I always print two off, one and a spare and take a photo of it.
I dont have to worry about losing the Orange ticket.
If someone only has one electronic device and no access to a printer, I can see why they'd be reluctant.
But any such concerns would disappear if the rail industry replaced CCST ticket vending machines with ones that could print physical copies of e-tickets!
The point is that we do actually have a universal standard now (finally!) however some TOCs refuse to move to it, and no-one seems able to force them.... a move to universal application is some distance away !
That's not the fault of the technology!
e-tickets tell you what they are at a glance too.Personally I'm happiest with a card ticket (or on bogroll paper if necessary) which tells me what it is at a glance.