The Government's Digital Radio Action Plan, published last July, cites 2015 as an 'achievable target date' for the switch-off of FM transmitters so (theoretically at least) it would seem reasonable to assume that all local radio stations will be migrating to DAB fairly soon.
However that date is regarded by many observers as unrealistic. (The UK Government signed up to an international broadcasting agreement which committed the UK to completing the changeover to digital TV by 2001, so it's not hard to see how plans can get delayed by a decade or so!).
With DAB radio, each area is meant to be covered by three multiplexes (which are simply bundles of channels). Most areas now have the BBC national radio multiplex, as well as Digital One's multiplex, which carries national commercial radio. The third multiplex (or combination of multiplexes) is meant to carry both BBC and commercial local radio. It's the third multiplex that most arweas are still waiting for, but progress is being made:
http://www.radio-now....ex_launch_updates.htm
Chris