Meanwhile here in Europe DAB and/or DAB+ is getting more and more popular.
This type of broadcast is not used in the USA, a different standard is used called HD, as far I know.
Can it be used nation wide, are there many stations broadcasting?
I use a tiny rod antenna only. That’s enough
But it has to be placed on the right place. 
Here in München I can receive more than 60 stations, via DAB+ more than via FM.
(But there are only 2 with classical music)
Most new cars have it, and many (most?) big stains use it at some level. But I think the majority of radio is listened to in cars here, so that is the bulk of the market.
Not many people listen to the radio the same way they used to anymore. Most people use Spotify or another music service like apple or Sirius. But most of the people who listen to it listen to it in the car I would agree. My family still has radios in the house that we use but I can’t say the same for everyone else in the US
Arent there many small radio local stations?
These would be important listening to -> traffic reports.
been a long time I stopped using the FM / AM radio use … I use the Sirius XM (lot of offers now) and streaming on iPhone (and now Pixel) … FM does not seem to be a great option when you travel, with range issues. Sirius XM is a reliable one, being a Satellite Radio …
Haven’t listened to radio in a long time myself. The last time I actually willingly did was back when I was in India. I prefer Hindi songs so stick to my phone or CDs for that. I know Houston has a radio station for Hindi songs that we listened to in the car when we visited our relatives to just check it out but nothing in Georgia from what I know
FM /AM is used often, but I would say there is no more future in this kind of transmission.
This Sirius XM is like a pay TV, and as you said you run it by your phone.
Quite a useful option.
Same will happen to TV.
The importance of the public TV stations is decreasing.
young folks are using netflix etc.
By the way I trashed my TV many years ago and I am free now! 
Why should I waste my time with such useless “taklk shows” with our … (censored) politicians.