"History" didn't end, as Francis Fukuyama said it would in his 1992 book The End of History and the Last Man; his thesis was that with the end of fall of Communism, history as a record of war, strife, and struggle, would end, and as relations between nations relaxed, the world would transcend ideologies and other divisions and create a more harmonies planet motivated by cooperation. The complete triumph of the free market. That never happened, and the world is arguably more problematic than it's ever been. History is still with us, and the concept of genres will remain with us as well. I don't think musicians are thinking about "post-genre" ideas when they make music, as creation is a psychological process as much as a physical one. In such the act of creation, the artist (all kinds of artists) are thinking, I believe, less about what rules they can ignore or what boundaries they can transgress. More about what they can make use of, whatever it may happen to me, however unlike, dissimilar, glaringly awkward the styles, the parts of the creation, may seem to be.
Their goal is to bring things together, whatever influences them and strikes their fancy. The appropriate it, twist it, change it, synthesize to something new, a work of art is a representation that hadn't existed before. But whatever the result, critically praised or damned, the object remains connected to history and the genres from which it attempted to abandon. This new work gets identified, described, classified, cataloged, it gets a name, it becomes a genre whose particulars are known and yet malleable within each piece the artist creates. It's an old story; in music, musicians have been genre-jumping for decades. One of my first albums was EAST/WEST by the Butterfield Blues Band, in which an inter-racial blues band took on Indian-raga/Modal jazz improvisational methods. The achievement was influenced by another transgressive innovator John Coltrane, who stepped out of his bop lineage to change how jazz was performed. The examples are endless. "Post genre," ironically, seems to be a genre itself.
As long as musicians continue to, by choice, write and record songs that fall into specific categories and subcategories--blues rock, metal, rap-rock, fusion, reggae, ska, country-rock, the whole shooting match. Genres, as we've always understood, are not dead. An obsession filters through the academic and critical universe that likes to announce that some particular form or medium is mortal because times have gotten so strange. Technology is now so pervasive that genre distinctions no longer apply and that we are now free to mix and match our tastes at will. This implies we have been liberated from some horrible tyranny; these kinds of global pronouncements have little to do with what's happening in the trenches, as it seems consumers like their genres --with the implication that there are many genres they happen to enjoy for their differences from other forms of music they happen to like-- and artists, young and otherwise, strive to maintain the various traditions meaningfully and moving while at the same time perverting the stylistic limits of the respective song forms by tweaking it with musical ideas from other areas. This, of course, creates new genres that will have cool names to describe their distinction. Nothing has died. However well specific approaches fare in the marketplace, it's not accurate to maintain we are in some area that has transcended genres. They are, in fact, thriving.