Fallout 3, arguably, introduced a great new feature to Fallout in the form of the radio.
Hate him or love him, Three-Dog brought atmosphere to the game with his chit-chat about current events and the music in between.
New Vegas continued along this line, bringing more music, new DJs.
Fallout 4 will without a doubt stick to this concept.
However, while the music is certainly a great contribution, it's also somewhat limited in scope and variety. I understand the limitations - for one, a lot of the classics require licensing and fees and to have the proper "Fallout feeling" the music needs to fit the overall 1950s theme.
But does it? I mean what's to keep from having some low-key guitar player just strumming along in the world space somewhere, sitting around a campfire. Doesn't have to feel 1950-ish. The world of music generally has popular trends, but that doesn't exclude all other music from existing at the same time. Classical music could/should still be around.
Thoughts?
And as a bonus thought. I'd love for the ability to include music from Fallout 3 and New Vegas into the FO4 playlists. To extend the life-time of the radio ("Oh god, not that song again already!") and to cash in on fond memories from past games.