Well, that's a chicken-egg situation, cars won't get DAB+ radio's until there's DAB+ broadcasts and it won't really be accelerated until FM is closely on the horizon to be shut off.
Similarly it took quite a while for the first CD players to appear in cars, and a lot of older cars only had casette tapes, keeping casettes alive for quite a while longer just for car use.
I've actually got a iPhone to cassette interface (I would call it a cable, but one end looks like an actual cassette) in my desk drawer, so that I could play my music in my car.
Similarly it took quite a while for the first CD players to appear in cars, and a lot of older cars only had casette tapes, keeping casettes alive for quite a while longer just for car use.