You might want to change your focus somewhat. Try looking at what teachers are doing now, today, in their classrooms, the kinds of methods they're using, and whether or not those methods are working. That is, are they effective? If so, why, and can you add to it/them. If not, what's the problem and, if possible, can you suggest a way to improve it/them.
Here's a start:
Community Language Learning
The Silent Way
Total Physical Response
Read more here: Principles of L2 Teaching Methods and Approaches
Note that, an MA thesis shows you understand the problem(s). You're not supposed to come up with a new idea. You're supposed to work with what's already there.
Here's my advise: go ask your advisor if there is an area that s/he thinks you should focus on. It's a start.
Student or Learner