Taking where learners write from the most and are more comfortable writing strikes me as a logical starting point. It's like planning a drainage systen: first see where the water wants to go (or not) and then design accordingly.
Revisualizing Composition: Mapping the Writing Lives of First-Year College Students :: WIDE Research Center, Michigan State University
This white paper reports initial findings from a Writing in Digital Environments (WIDE) Research Center study entitled Revisualizing Composition: Mapping the Writing Lives of First-Year College Students. These initial findings are drawn from a survey of students enrolled in writing classes at a sample of US postsecondary institutions.