The final cut of the 8th episode of the Tesla Motors Club Podcast, featuring Balazs Biro, of the prominent Hungarian EV channel Villanyautósok, is now available. You can watch it now on YouTube or listen to it on all major podcast networks.
Its an expensive way of doing it but upgrading the MCU and optioning the radio module for an extra £400 or so would get you DAB but a total cost of around £2k for a car worth maybe in the high 20k/low 30k might be a tough expensive.
To answer your other question, DAB came with the premium sound option until mid 2015 when it became standard fit.
I don't know how you'd source one or whether it is even a skilled DIY option (as the software would need to be enabled on your car and I know people have had the MCU2 upgrade done with the radio module and Tesla forgot to enable it), but if it was possible, then I imagine there are lots of the modules being ripped out of cars when they have the MCU2 upgrade done.