Since art is created by humans, it will keep changing as long as humans keep changing. With every new historical event, new art forms are created--like when exiled Jewish artists wanted to find a way to portray the horror of the Holocaust. With every new decade, styles and art forms change--like with the creation of pop art. Humans as a species are perpetually developing new ideas, materials, interests, and perspectives. This makes art an ever-fluid and changing thing.
I do not believe humans will ever stop changing and developing. History teaches us otherwise. Even with every old style or fad that makes a come-back in our culture today, there are hundreds of new styles and fads. As a result, art will never stop changing and developing.
So, to answer Mary's question, I think the only point in which art will cease to grow will be when humans cease to populate the earth. Until then, it will not stop growing. I'm glad, though. I think it's a beautiful, wonderful thing. :)
Question in response (even though nobody will answer it because it's the last blog): What time period do you think had the most inspiring visual art?