It's interesting how music has moved through phases in the last century, sort of making it up as it goes along. In the nineteen-thirties, Gershwin wasn't considered (by many) to be a "classical composer" because he came from a background of jazz and "show tunes"; his music was too improvised. When Copeland turned to incorporating jazz styles, he was cautioned for getting too "low brow," too free with his music. Classical music needed to strive for something new, not succumb to the music of the masses. For years the two worlds seemed to be separated by some arbitrary class structure.
However, jazz has become so much a part of our musical consciousness that "classical" musicians are incorporating elements of it in their music all over the place. Many of the biggest names in "pop/jazz" world reference their classical roots (Beyoncé Knowles). According to a NY Times music review, Bill Frisell wrote a series of string quartet pieces incorporating a host of different jazz elements, most notably improvisation. André Previn is considered a "superstar" in both forms. Brian Ferneyhough writes that elements of his Second String Quartet are to sound "improvised" even though the music is meticulously scored. More and more respected composers are using improvisational sections in their classical music. However classical musicians still tend to balk at this inclusion as it is unfamiliar territory, the world of improvisation is not black and white, but shades of many different colours.
This wonderful article on Solarfantasy on the History of Jazz and Classical Music discusses the idea that Bach was a master improviser. This skill was expected of organists of his day. Liszt was also extremely skilled at improvisation occasionally performing impromptu concerts completely improvised. Czerny speaks of Beethoven coming in one afternoon and playing nearly the entire third movement of his piano sonata number 29, Opus 106 before he began writing down the notes, and there were few changes from what we have now as what was played that afternoon.
Numerous composers I have spoken with, or read their bios on their blogs speak of jazz as an influence in their musical style, or they speak of improvising at the piano when creating a piece (or both). I was fortunate enough to hear Rohan de Saram perform at the Sound Festival in Aberdeen with Fred Frith in a half hour "jam" session, that was amazing. Earlier at the festival, in Fred's Master Class on Improvisation, he spoke of the need for classical musicians to explore improvisation and for composers to incorporate it as a means to better meld the performer's interpretation and the composer's music.
What is also interesting is the growing acceptance of jazz music in the classical world. Jazz musicians have often taken classical melodies and "jazzed" them up, or, as evidenced by the Ornette Coleman Quartet, taken jazz tunes to new levels treating them as equals to the classical melodies they embelish - as they did with Gershwin's "Embraceable You". If you google "Gershwin" and "Rhapsody" in the news and you'll find an amazing assortment of upcoming concerts featuring this piece.
Maybe the time has come when the search for new music has come upon the idea that it's been with us all along, we just need to relax and "go with it."