I recognize it is a bit more difficult to deal with buffer. But, do you really want JavaScript developers for witch this would be a technical barrier to make gulp plugins ? It took just a few minutes to convert the marked plugin (tests included).

On the user side, the API will be the same. I just asked my JS user group to look at converting our Grunt tasks to a Gulp one and the poor quality of Gulp plugins has be argued as a frontier for users (https://github.com/ChtiJS/chtijs.francejs.org/issues/25#issuecomment-31532951).

My opinion is that it is not a bad thing to move JavaScript beginners away from plugin development. Recommending to use streams instead of buffers is a step in the right direction either for performance than for plugins quality.