Acceptance of all credit cards is a must, and needs to be at the top of the development list. Various rumours abound that the banks are not at all happy at continuing to process offline payments and the various authorisation issues that come with them. The railway must be the worst offender by a long way.
Had joined-up thinking and common sense not been outlawed on the modern railway, somebody might have suggested building into the GSM-R system an 'auxiliary' facility, which might have used the blanket coverage capability to carry additional secondary data like ticketing systems. Alas, such a suggestion is outrageous of course...
As for the kit itself, it needs to be extremely tough - they get dropped regularly, and they suffer some heavy abuse. A tablet device alone would last a few months max before becoming corrupted by the constant shock to the hard drive etc, or be wrecked due to the screen smashing on a regular basis, assuming it didn't get nicked first. A benefit of the current set-up is that from the public's perspective the thing is just a strange, alien ticket machine - I imagine theft would have been rife in the early days if the scroats knew what was actually in there was a natty little Casio palmtop running Windows; nowadays of course you'd be lucky to get a fiver for it, it's old-tech indeed.
Replacement is long overdue, but what the TOCs really need to do is club together and get the contract handed to somebody else, with a proviso that the new design uses readily available components wherever possible, supplied at a sensible price. Alas it won't happen, and Atos (or 'Wordline - an Atos company') will no doubt continue to charge the railway joke prices for the next 10 years - 50 quid for a printer battery anybody? Eight pounds for a little plastic stylus? (you can buy a pack of three in pound shops). The best one is the fixed fee of around 300 quid every time one needs to go back for any sort of repair. Hang on, so it's your kit, which we have no choice but to lease from you at whatever ludicrous price you decree, it's ancient, outdated and woefully unreliable - and you get to bill us a fortune every time it packs up!? Think I might start a ticket machine racket myself! And all of this in an industry which is desperate to shed staff to cut costs! Scary stuff...