These solutions would be more long-term and would definitely require a fair amount of investment in both new software and hardware. However, I do feel that they would very much improve the user experience.
One solution to speeding up the process and making the fare buying option faster overall would be to overhaul the whole system. An option would be to make everything go through a disposable CharlieCard instead of having 2-3 different ticket options that all serve the same purpose (See the MetroCard system of the NYC Subway).
With smartphones becoming much more prominent in our everyday lives, why not give the option to pay with ApplePay or even a new app that allows the user to simply get a QR code on their phone scanned to pay for their ticket?
An even better smartphone solution would be to allow users to simply buy tickets/fares on an app on their smartphone. This is actually a system the MBTA uses for their commuter rails. Making it work on the subway would simply require a way in which the turnstiles/gates could interact with the user’s phone.