Andy Warhol could have expressed himself in any medium. He chose painting (or at least a medium that appeared on its surface to be painting), perhaps by accident or by design, but whether he chose painting for this reason or was merely successful because he chose correctly, we may not know, but at the time he worked painting was the one medium where an artist would be taken seriously, what they had to say about society would be taken seriously in the medium of painting. He could have expressed his prescient views on celebrity and mass media by carving little dolls or collages, but he chose painting, I believe because that is the medium society would take seriously and pay attention to. If he didn't understand that, he was ignorant of the art world and society from the mid-twentieth century to the end of the twentieth-century. Only now with the information age are new art forms emerging that make painting, novels, movies obsolete.
A great artist does not care what medium they work in. They only care, as Warhol understood, that the job of the artist is to achieve a unity with their times and produce works that are completely in tune with what is happening in society, only slightly before society begins to realize what is happening. Celebrity was coalescing into a powerful social force in Warhol's time and he recognized it before anyone and found a means of expression for his recognition.
If you want to be a great artist today, you will not want to paint with oils like Picasso, abuse industrial sign printing technology like Warhol, or take photographs, you will want to discern the unique changes taking place in society in your time and create works that show people that. I don't know what they are or what medium it will be, but I can take some guesses. Social networking seems to have the force and weight that celebrity once had in 20th century society. It is emerging as a phenomena with the potential to completely reorganize authorship, art and life in the next century. I know it seems small and like a fad, but it there are profound changes taking place when you start to a) make authorship easy for everyone and b) make it easy to mix content from more than one person. When it becomes commonplace and ubiquitous for people to have other people's works of authorship displayed mixed in on their "social network profile page" (an ugly phrase, but what do you call it other than "my page?"), it changes the nature of authorship. It used to be clear who authored a work. Now it is not so clear or at least confusing to someone who grew up with books signed by an author, news stories bylined by the reporter. But the times are changing. It seems normal to young people to have other people's content show up mixed in their own, to see pages with content contributed by many people all jumbled together. I forsee a shift in the way people gain status, not just through works of authorship, which the networked world breaks down (devalues), but through becoming essentially editors of their own personal magazine...the profile page. It is a logical extension of your friends appearing on your social network home page, a simple step from that to your friends works of authorship appearing on your home page. This is like a "digg/slashdot/kuro5hin" site in miniature, where you get to approve or disapprove the content (stories, photos, etc.) appearing on your page. Users on flickr, gain status not just through authorship, but through association. The user with the most authors in their "stable" or contacts list or whose content appears on their page, wins. We already see the editors of these pages begging authors to "join their group" or become friends so that the best shared content will appear on their page.
I experimented with this in the late 1990s but it never went anywhere since I didn't push the project to completion. I was held back by fears, which I attributed to worries over vandalism (it was wiki-style), but which I believe were existential fears about authorship, the breaking down of authorship that might occur when one could easily refer to or include other people's content in your own through tagging (which was how it was to work).