Dissertation Planning - Blended Learning

In the next few weeks I need to submit a protocol for my dissertation, which, all being well, I should be starting in September.

However, I'm struggling to decide what angle to take.  I know I want to do online learning / blended learning, but the focus is difficult to pin down.  I could work with a diverse group of students - ranging from my youngest (school leavers) in an FE setting through to mature learners in a community education setting, and look at the different levels of engagement in online learning from the different groups.  Alternatively, I could focus on a single cohort of students, and dig deeper into the individual experiences they have with online learning, and whether these are successful or not, and why.

I have started a literature review, but I think I've got some way to go with this.  So far, I have identified that Gilly Salmon's Five Stage Model forms an excellent starting point, but that less research has been done on student engagement with a specific task and that there is more focus on social engagement.

Perhaps starting with a well structured task (using the Five Stage Model) and rolling that out to all cohorts (in a relevant format) is the way to go.  This will then form a comparison of different cohorts and levels of engagement, and perhaps suggestions as to how to promote the benefits of online learning to different groups of students.

Any thoughts or suggestions would be gratefully received.  Is there a gap somewhere that needs investigating?  Feel free to comment!