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The latter part of what you suggested - the pre-concert talk - is a very common thing to have now, and often it's a 30-minute thing. Program notes are also getting better and better about this. People will also often talk about the context when they give recitals.

As to clapping: As late as the late 1800s, it was okay to clap during the loud parts of the song. Baroque music also often has long cadenzas that end in a big trill, which was a signal for the crowd to go wild. I agree about getting less strict about this, and historically things were less strict. At the same time, I recently saw a performance of Tchaikovsky 6 where the audience started clapping between the last two movements (a triumphal march followed by a tragic final movement), and a large part of the energy of the piece was lost from the audience doing this. I think this rule mostly comes from the audience not understanding when not to clap.

Also, lots of classical music is done in environments that aren't concert halls and these are much looser about the etiquette. A concert hall is a nice place to go, and many people go on dates at concert halls, and a lot of the vibe for the audience comes from the fact that people dress up for the occasion.