Let's start with an analogy: The UK Government signed up to an international agreement (because radio waves don't stop at borders) committing the UK to completing the switch to digital TV (and freeing up the old analogue frequencies for other uses) by 2001. So, even after entering into a firm commitment, we're currently running 11 years behind schedule!
As far as digital radio is concerned, there's currently no firm commitment on any date for a complete switchover. (Indeed, there will never be a true 'switchover' as the VHF-FM frequencies will still be used by low-power stations, such as community radio). The Government announced a 'target date' of 2015 for all of the big radio broadcasters to go 'digital only' but that's now clearly impractical. The target date will probably get put back to around 2020 (and then, like delay with digital TV) take another decade or so to actually come about.
However devices which allow analogue car radios to receive DAB stations are already on the market (and have been for several years):
http://www.amazon.co....smitter/dp/B0012GLXMU
Chris