Last weekend on public television I saw a fantastic biography about Pete Seeger, the influential folk singer and activist. Throughout, Seeger stressed his desire to sing with people, not to people — motivating music as a collaborative endeavor. This sentiment is echoed in the accessible book, This is Your Brain on Music, which points out that music as "performance" by people on a stage to other people seems to be a fairly new thing. Traditionally, music was a group activity that was not reserved for those of express "skill" and training.
Drawing is much the same way. We often make a huge break between those with or without "talent" — resigning people to the misperception that they "can't draw", when really our biological endowment ensures that we all can draw. Really what is at issue is a level of fluency, and most people just don't develop with the proper exposure or practice.
Language, like this sense of music, is entirely collaborative. And, it is learned collaboratively, unlike most learning of drawing. In some cases, drawing might be instructed, often very well, though this is far from simply being interactive in the sense that you learn just by participatory immersion.
On a productive sense, drawing also is highly non-collaborative in our modern life. Belonging to a print-culture, most drawers and readers are separated by huge distances of space and time. This isn't always the case though. Sand narratives by native communities in Australia are highly interactive, drawn in real-time communication.
Humans are an intensely social animal, and my gut tells me that nearly all of our expressive capacities developed and thrive in such collaborative interactions. The question is: how in our modern ecology can we facilitate such usage for visual language? Will we have to rely on technological breakthroughs (ex. digital whiteboards), or can it grow organically without the crutch of engineering?
For those interested in more about this, my article from a few years ago "Interactive Comics" probed a lot of these ideas.